Released versions of package CRT
                                                                   
                                                     
Released versions:
    1.00 (1988, June):  Preliminary version, contains only subroutines
            for model specification, no complete ray tracing
            subroutines.
                                                     
    2.00 (1990, February):  Common release with model specification
            routines.  First consistent version of the ray tracing
            program.  The routines determining the take-off parameters
            of rays are awfully primitive.  Poorly debugged.
                                                     
    3.00 (1991, January):  Common release with model specification
            routines.  New version of the file 'rpar.for' determining
            the take-off parameters of rays:  one-parametric
            boundary-value ray tracing.  Principal errors removed in
            files 'ray.for', 'raycb.for' and 'trans.for'.  Some of the
            points of intersection of rays with the given surfaces may
            be selected for storing the computed quantities - minor
            changes in files 'ray.for' and 'writ.for'.
                                                     
    4.00 (1992, December):  MODEL and CRT packages has been split:
            'raycb.for': Split into 'means.for' (MODEL) and
              'raycb.for' (CRT).
            'crt.for': Split into 'crt.for' and 'crtin.for', name of
              the data set CRT read from the * unit.
            'ray.for': Indices of end surfaces supplemented with the
              signs, boundaries of the computational volume enabled to
              be storing surfaces.
            'raycb.for': *** Considerable changes and corrections. ***
            'trans.for': Corrections for nearly normal incidence, and
              for weakly refracted or nearly grazing rays corrected.
            'init.for': Definition of material parameters, and of the
              signs of auxiliary surfaces at the initial points
              corrected.
            'rpar.for': Reading the data for an auxiliary surface
              specifying the profiles enabled.
            'writ.for': Specification of the names of output files
              slightly generalized, independent variable X along rays
              added to the output files, some other minor changes.
            'scropc.for': Minor changes.  E.g., refreshing wave index
              on the screen added, renumbering of colour indices
              removed (unfortunately, the renumbering may be useful on
              some computers).
            *** new FORTRAN77 source code files ***:
            'calcomp.for': CalComp to GKS graphic interface.
            'ap.for': Applications and processing of the results of
              complete ray tracing, only the first 1/3 of subroutines.
            'inv1.for', 'inv3.for', and 'inv4.for': Provisions towards
              a tomographic inversion.
                                                     
    4.10 (1994, January): 'ap.for' split into 'ap.for' and
            'apvar.for'.
            'crtin.for', 'code.for', 'ray.for', 'trans.for',
            'init.for', 'rpar.for', 'writ.for', 'calcomp.for',
            'ap.for', 'apvar.for', 'inv1.for', 'inv3.for', 'inv4.for':
              Error messages, previously generated by statements like
              STOP 'Error...', are now generated by PAUSE 'Error...'
              followed by the STOP statement, in order to suspend the
              batch files in the case of error (the date of
              subroutines not updated).
            'crtin.for', 'code.for', 'ray.for', 'init.for',
            'rpar.for', 'writ.for', 'scropc.for', 'calcomp.for',
            'ap.for':  Each BLOCK DATA subprogram has been declared
              EXTERNAL in the subroutine designed to read or
              initialize the data shared.  The subroutine is the first
              subroutine in the corresponding file, after the BLOCK
              DATA subprogram, and was always assumed to be called
              before the data in the corresponding common blocks can
              be used.
            'calcomp.for', 'ap.for':  External procedures declared
              EXTERNAL.
            'code.for':  Subroutine CODE1 has been corrected and
              updated - determination of the common parts of
              elementary waves enabled.
            'rpar.for':  Several bugs fixed.  Subroutines restructured
              in order to separate one-parametric shooting from the
              parts useful also for possible future upgrade to
              two-parametric shooting.  Specification of profiles
              along coordinate planes simplified.  Profile coordinates
              in a separate file enabled.
              *** change in input data: Index of the second X-function
              (receiver coordinate) reserved for future extensions ***
            'writ.for':  Generation of error message 557 corrected.
              Indications IEND,ISHEET added to the output files with
              initial points of rays.
            'ap.for':  Wrong second travel-time derivatives fixed.
              Statements dealing with curvilinear coordinates denoted
              by '*' in the first column.
            'crt.for', 'code.for', 'raycb.for', 'init.for',
              'rpar.for', 'writ.for', 'scronul.for', 'scropc.for',
              'calcomp.for', 'ap.for', 'apvar.for', 'inv1.for':  Other
              minor fix-ups and changes.
            *** new FORTRAN77 source code files ***:
            'crtray.for':  Program converting the unformatted output
              of program CRT into formatted files with rays suitable
              for plotting.
                                                     
    5.00 (1996, September):
            'crt.for': Minor update.
            'code.for': Minor correction of comments.
            'raycb.for': Updated.  Subroutine PSHIFT considerably.
              Boundaries of computational box enabled as storing
              surfaces.
            'trans.for': *** Reduced amplitudes corrected. ***
            'init.for': *** Updated, input data changed. ***
               In particular, initial line and surface fixed.
            'rpar.for': *** Considerably corrected and updated, input
              data changed.  Split into 'rpar.for' and 'rp2d.for'.
              Calls to 'rp3d.for' enabled. ***
            'writ.for': *** Updated. Input data changed. ***
              Indication IREC added to the output files with initial
              points of rays, files with indices of rays forming
              homogeneous triangles in the ray-parameter domain now
              generated.  Check for nonexisting rays supplied.
            'scropc.for': Updated.  Default plotting units switched
              to inches.
            'ap.for': *** Considerably corrected and updated. ***
            'crtray.for': Considerably updated.
            'plotvdi.for','ploth.for','plotvax.for': Discarded.
            'calcomp.for': Moved to package MODEL.
            's1-code.dat': Renamed to 'code1.dat'.
            's1-crt.dat','s1-rpar.dat','s2-crt.dat': Changed, renamed
              and moved to subdirectory 'len'.
            'inv1.dat','points.dat','ftt.dat': Changed, renamed and
              moved to subdirectory 'u2d'.
            'inv3grid.dat': Renamed to 'inv3.dat'.
            '*.pre': Updated, renamed to 'prem*.*', and moved to
              subdirectory 'prem'.
            'crtpc.bat': Discarded.
            *** new ***:
            All files converted from UPPERCASE to both UpperCase
              and LowerCase (for better reading and Unix systems),
              INCLUDE statement introduced for COMMON blocks.
            '*.inc': Include files with COMMON blocks.  SAVE statement
              is now used consistently for COMMON blocks
            All files with main programs supplemented with the INCLUDE
              statements to include all files with called subroutines
              to simplify the compilation and linking considerably.
            MS-DOS batch files supplemented with corresponding Unix
              scripts.
            'rp3d.for': Subroutines to control the two-parametric
              shooting algorithm for 3-D two-point ray tracing.
            'scronum.for'... New simple basic version of the screen
              output subroutines.
            'crtout.for','ttsort.for','crt2p.for','crtpts.for':
              Subroutines and programs to convert or process the
              unformatted output of program CRT.
            'green.for': Program to convert the output of program CRT
              into the ray-theory elastodynamic Green function.
            'greenss.for': Program to read the ray-theory
              elastodynamic Green function and to generate time-domain
              synthetic seismograms or frequency-domain response
              functions.
            'ss.for' and 'sp.for': Programs to generate and plot
              synthetic seismograms, adopted from package SW84,
              updated for the list-directed input and the GSE data
              exchange format, commented.
            'srpcrt.bat','lcrt.bat': Sample MS-DOS batch files.
            'len','prem','elf1','u2d': Subdirectories with examples of
              input data corresponding to different seismic models.
                                                     
    5.10 (1997, October):
            *** probably not all changes are listed here ***
            'inv1.for' split into 'soft.for', 'inv1soft.for' and
              'inv1tt.for'.
            'soft.for', 'inv1soft.for', 'inv3.for','inv3.dat','inv4.for'
              moved to package MODEL.
            'crt.doc' renamed to 'crtdoc.htm' and revised.
            'lcrt.bat' renamed to 'fcrt.bat' and revised.
            'code.for','ray.for','init.for','rpar.for','rp2d.for':
              BLOCK DATA subprograms cancelled.
            'crtpts.for','green.for','greenss.for','ss.for','sp.for',
              'inv1tt.for': Memory managed by means of 'ram.inc'.
            Descriptions corrected and updated in most files.
            All error descriptions moved towards the corresponding
              reporting statements.
            Errors renumbered in some files.
            Warnings written to log files instead of the console.
            'rpar.for': KMAH index included also in the history of an
              unsuccessful ray.  New option to include or not the
              boundaries of the computational volume into ray histories.
              Default input value of IPOINT changed.
            'rp3d.for': *** Considerably corrected and updated. ***
            'ap.for': Reading just initial points enabled.
              *** Severe bug fixed in AP21. ***
            'writ-s.dat' renamed to 'writsrf.dat' and 'writall.dat'
              supplemented.
            *** new ***
            All Fortran files supplemented with HTML references.
            'rpplot.for': Plotting ray parameters.
            'crt2d3d.for': Converting 2-D results of CRT for MTT.
            'mtt.for': Interpolation within ray cells.
            'mttgrd.for': Converting multivalued travel times produced
              by program MTT into several singlevalued grids
              corresponding to individual ray histories.
                                                     
    5.20 (1998, October):
            All error messages in the Fortran files, previously
              generated by statements like PAUSE 'Error ...', are now
              generated by CALL ERROR('...') in order to enable to fit
              the error handling for a particular computer by editting
              file 'error.for' (the date of subroutines not updated).
            Most warning messages in the Fortran files, previously
              generated by statements like PAUSE 'Warning ...', are now
              generated by CALL WARN('...').
            'crtdoc.htm' split into 'crtdoc.htm' and 'crtver.htm',
              list of files moved to 'crt.htm'.
            'ss.for','sp.for': *** Moved to package FORMS. ***
            'crt.for': Subroutine LUWARN moved to '../forms/error.for'.
            'raycb.for','init.for','crtpts.for':
              *** Severe bugs fixed. ***
            'rpar.for': Now writing the table of ray histories and
              optionally checking whether a ray satisfies the whole
              code.
            'rp2d.for': Revised.
            'rp3d.for': *** Considerably revised:  Distance of
              a two-point ray from the receiver may now exceed XERR
              (with warning in logout file), some bugs fixed. ***
            'rpplot.for': *** Input data changed *** (name of output
              plot can be specified).  CRT output files containing more
              than one elementary wave may now be used.
            'rpsymb.for': Bugs causing stack overflow in PostScript
              fixed.
            'mttgrd.for': *** All output grids (data cubes) now written
              into a single file by default, N4 appended to input SEP
              file. ***
            'ray.for': Comments updated.
            'crtout.for','rparc.inc','rp2d.inc','rp3d.inc',
              'rpplot.inc','mtt.inc': Minor corrections.
            'ap.for': Bugs in subroutines AP00 and AP03 fixed.
            'inv1tt.for': A bug fixed.
            *** new ***
            All MS-DOS batch files '*.bat' and Unix scripts '*'
              replaced by corresponding Perl scripts '*.pl' or by
              history files '*.h' containing the lines specifying how to
              run the programs.
            'crtcart.for': Program converting rays calculated by program
              'crt.for' from curvilinear to Cartesian coordinates,
              which are required by 'mtt.for'.
            'mtt.for': *** Considerably revised: Bicubic travel-time
              interpolation introduced, errors on sides of ray cells
              removed, 'indexx.for' used to speed up sorting of ray
              tubes, interpolation of slowness vector enabled, minor
              errors in caustic regions connected with number of roots
              of cubic equation removed. ***
            'green.for':
              *** Input data changed to SEP format ***
              Calculating frequency-dependent elementary Green functions
              using coupling ray theory in anisotropic models.
            'wan.for': Subroutines for coupling ray theory in weakly
              anisotropic models.
            'greenss.for':
              *** Input data changed to SEP format ***
              Able to read frequency-dependent elementary Green
              functions (e.g., of coupling ray theory for S waves).
              May include the response of the transmission through a
              stack of fine horizontal layers at each receiver location.
                                                     
    5.30 (1999, June):
            'crt.for','crtin.for','init.for','rpar.for':
              *** Main input data changed to SEP format ***
            'init.for': Updated to correspond to the new version of
              subroutines BLOCK and BLOCKS of file 'model.for' of
              package MODEL, bug in subroutine SPHERE for INIPAR=3
              fixed, *** input data changed (SEP format) ***
            'raycb.for','rpar.for','rparc.inc','rp3d.for','rp3d.inc':
              *** Control of the width of ray tubes enabled. ***
              Error reports in 'rpar.for' improved.
            'mtt.for','rpplot.for':
              *** Main input data changed to SEP format ***
            'mtt.for','mtt.for': *** 2-D computations enabled (without
              crt2d3d).  Interpolation of new quantities supplemented.
              Several bugs connected with rays of zero length fixed. ***
              Interpolation in tetrahedra possible after minor editing
              the code.
            'green.for': The bug related to the names of output files
              of program 'crt.for' fixed.
            'wan.for': *** Computation of travel time corrections fixed.
              New criterion for the maximum error of propagator matrix.
              Models with structural interfaces enabled (but not fully
              debugged!) ***
            'greenss.for': Fatal bug when writing zero frequency
              response function fixed.
            'scropc.for': A bug fixed.
            'ray.for','writ.for','ap.for','rpsymb.for':
              Minor correction of comments.
            'code.dat' renamed to 'code2.dat', because it contain codes
              of waves reflected at the first and second interface.
            'rm/rm-mod.dat': Free space simple block added.
            'crt.h', 'len/lenb-rpa.dat', 'len/lenz-rpa.dat',
              'elf1/elf1*crt.h':
              Created to reflect the conversion of input data for
              program crt.for to the SEP format.
            'srpcrt.pl','crt.dat','rpar.dat','len/len-crt.h',
              'len/lenb-crt.h', 'len/lenz-crt.h', 'len/leni-mtt.h',
              'prem/prem-crt.h','u2d/u2d-*.h','rm/rm-fd.h','qi/qi-ss.h',
              'elf1/elf1*crt.dat','elf1/elf1*.pl','98/98-mtt.h',
              '98/98-ss.h','*/*-crt*.dat','*/*-rpa*.dat':
              Modified to reflect the conversion of input data for
              program crt.for to the SEP format.
            'len/len-crt.h', '98/98-ss.h':
              *** Upgraded to generate 3-D VRML97 representation of
              two-point rays together with structural interfaces. ***
            *** new ***
            'code.dat': Code of P wave transmitted at all interfaces
              (the most common wave code).
            '98/98-mod.h', '98/98-cam*.dat' and '98/98-dli*.dat':
              History file to generate 3-D VRML97 representations of
              structural interfaces and velocity distribution in model
              98, and the corresponding data desribing initial positions
              of the camera and the directional lights.
            'wrl': Subdirectory with examples of 3-D VRML97
              representations of rays with structural interfaces.
                                                     
    5.40 (2000, May):
            'crt2d3d.for', 'crtray.for', 'crtpts.for', 'srpcrt.pl':
              *** Input data changed to SEP format. ***
            'mttgrd.for':
              *** Input data changed. ***
              Multiple files from * device moved to the history file.
            'crt.htm': Considerably revised.
            'crtdoc.htm' discarded (information moved to 'crt.htm').
            'crt.for','init.for','initd.inc','rpar.for','scronum.for':
              *** Ray tracing for multiple sources enabled. ***
            'init.for': A bug in initialization of IY(11) fixed.
            'rpar.for': *** Severe bug in the determination of ray
              histories fixed.  Severe bug in the estimation of the
              widths of ray tubes fixed. ***
            'rp2d.for': Creation of ray tube limited by non-existing ray
              during initial-value ray tracing fixed.
            'rp3d.for', 'rp3d.inc': Several bugs fixed.
            'scropc.for': Enter from standard input to confirm erasing
              of the ray diagram of each elementary wave is no longer
              required, but may optionally be enabled.
            'apvar.for': Subroutine AP28 moved to 'ap.for'.
            'rpplot.for': Minor corrections.
            'mtt.for' split into 'mtt.for' and 'mttq.for'.
              File 'mttq.for' contains specification of interpolated
              quantities and may simply be editted in order to add new
              user-defined quantities for interpolation.
            'mtt.for': Some bugs, mainly in 2-D interpolation, fixed.
            'mtt.inc': Minor changes.
            'mttq.for': Interpolation of width of Gaussian beams added.
            'mttgrd.for': Numbers in generated filenames decreased by 1.
            'green.for': *** Multiple elementary waves enabled. ***
            'greenss.for': A bug related to attenuation at zero
              frequency fixed.
            'inv1tt.for' renamed to 'invtt.for' and *** considerably
              updated. ***
            'code.dat' renamed to 'codep.dat' and 'code2.dat' to
              'codep2.dat'.
            Subdirectories with the data for particular models moved to
              new package DATA.
            'len-src.dat' moved to package DATA.
            'rpar.dat' renamed to 'len-rpar.dat' and moved to package
              DATA.
            'crt.h' and 'crt.dat' renamed to 'len-crti.h' and
              'len-crt.dat', updated and moved to package DATA.
            'wan.for':
              Cosmetic changes.
            'crtin.for', 'writ.for':
              Comments updated and corrected.
            *** new ***
            'calcompx.c': CalComp to Xlib (X Window) interface.
            'crtx.mak': Makefile to compile and link 'crt.for' with
              'calcompx.c'.
            'wfsrf.for', 'wfsrf.inc': Program to generate wavefronts
              composed of polygons for display purposes.
                                                     
    5.50 (2001, June):
            'crtin.for','writ.for','writ.inc','scronum.for',
              'scronul.for','scropc.for','ap.for','pointc.inc':
              *** Output files of ray tracing by program 'crt.for'
              supplemented with source index ISRC. ***
            'crt2p.for', 'crtcart.for': Minor changes related to reading
              of the output files of program 'crt.for'.
            'ray.for':  Comments updated.
            'rp3d.for': *** Error in coverage of ray domain fixed. ***
            'mtt.for': *** Second derivatives of the complex-valued
              travel times of Gaussian beams, which were specified
              by constant real-valued parameters in version 5.40, may
              depend on two-way travel time and ray parameters, and may
              be specified on an optional ray-parameter grid. ***
            'mttq.for','mttq.inc': Subroutines of file 'mttq.for' are
              now used also by program 'wfsrf.for'.
            'mttwf.inc': New file with declaration of common block used
              by both programs 'mtt.for' and 'wfsrf.for'.
            'wfsrf.for', 'wfsrf.inc': *** Many new quantities may be
              computed along wavefronts and written to output file. ***
              List of the quantities, which may be computed
              along wavefronts, has been unified with program 'mtt.for'.
              Subroutine file 'mttq.for' is now used by both 'wfsrf.for'
              and 'mtt.for'.
            'crtpts.for': *** Parameter ISRC renamed to KREC. ***
            'crtpts.for','crtray.for','crtout.for': New parameters KSRC
              and KTWO.
            'green.for','wan.for': Maximum error of the quasi-isotropic
              projection of the polarization vectors now checked and
              reported.  Various kinds of quasi-isotropic approximation
              now enabled for testing purposes.
              *** New input parameters ERRQI, QICHM, QITT, QIDT. ***
              *** Tests of the coupling ray theory calculations in
              models with structural interfaces enabled. ***
              Error messages corrected.
            'greenss.for': Source coordinates in the comment lines of the
              GSE file now identified by parameter names X1SRC, X2SRC
              and X3SRC, instead of XS1, XS2 and XS3.
            'invtt.for': Calculation of the checksum fixed.
              Minor corrrections of error messages and screen output.
            'srpcrt.pl': ISRC changed to KREC.
            *** new ***
            'ap.for','apvar.for': Simultaneous quadrature of several
              sets of equations by several invocation of subroutine AP28
              at each point of ray has been enabled, which is important
              for optimization of the shape of Gaussian beams.  Optional
              calculation of the variations of the line integral of the
              density for the gravimetric inversion has been included.
            'gbopt.for': New program to calculate quantities for
              optimization of the shape of 2-D Gaussian beams for
              prestack migrations.
                                                     
    5.60 (2002, May):
            'crtin.for': Input data description updated.
            'ray.for': Comments updated.
            'rp2d.inc': Comments updated.
            'rp3d.for': Error messages and comments updated.
            'writ.for': Description of the input data files improved.
              *** Output files are written only if the first components
              of their filenames are not blank. ***
            'writ.for','rp2d.for','rp3d.for': Subroutine WRITA renamed
              to WRITTR.
            'writ.for','rpplot.for','crt2d3d.for','mtt.for','wfsrf.for':
              *** Identification of individual elementary waves in file
              'CRT-T' coded. ***
            'scropc.inc': Comments updated.
            'ap.for': *** Serious bug in AP28 fixed. ***
            'ap.for','green.for','wan.for','mttq.for': Subroutine AP21
              calculating the Green function upgraded to optionally
              consider correct eigenvectors of the Christoffel matrix.
              *** Program 'green.for' now need not apply the quasi-
              -isotropic approximation of the polarization vectors. ***
            'rpplot.for': *** Parameter NWAVE renamed to IWAVES. ***
            'crt2d3d.for': Description of input data improved.
            'mtt.for','mttq.for':
              *** Parameter NWAVE renamed to NWAVES. ***
              Program now works with all the elementary waves stored
              in the corresponding CRT output file 'CRT-T'.
            'wfsrf.for': Description of input data improved.
            *** new ***
            'rp2d.for','rp3d.for','rp3d.inc','writ.for','writ.inc':
              Writing of the CRT output file 'CRT-B' with indices
              of boundary rays coded.
            'green.for','wan.for': Optional calculation of second-order
              perturbations of anisotropic travel times of S waves.
                                                     
    5.70 (2003, May):
            'crt.for', 'crtin.for', 'dcrt.inc', 'initc.inc',
              'rpard.inc', 'rparc.inc', 'calcompx.c', 'crtx.mak':
              Formal updates related to new file 'scro.for', see below.
            'writ.for': Comments updated.
            'rp2d.for': Small bug in searching for boundary rays fixed.
            'rp3d.for': Small bug in internal evidence of two-point rays
              fixed. *** New parameter PRM0(5) for control of the
              distance of two-point rays from the receivers. ***
            'ap.for','apvar.for': Minor updates of error messages.
            'crtcart.for': *** Fatal error (wrong number of unit for
              reading) corrected.  Output files supplemented with source
              index ISRC. ***
            'crtpts.for': Comments updated.
            'green.for','wan.for': INCLUDE commands moved from 'wan.for'
              to 'green.for'.  Description of the output file QILST
              updated.
            'greenss.for': A minor change in output format.
            'invtt.for': *** Source and receiver points may now be
              specified in multiple files, instead of a single file.
              Structural interfaces may now be inverted.  Structural
              interfaces and material parameters may be inverted
              separately.  Input parameter DIST must now be specified.
              *** Error messages and comments updated, declaration of
              variables improved.
            *** new ***
            'crt.for', crtin.for', 'dcrt.inc', 'raycb.for', 'init.for',
              'initd.inc', 'initc.inc', 'rpard.inc', 'rparc.inc':
              Ray tracing of the anisotropic common ray coded for the
              models without structural interfaces.
            'init.for', 'initd.inc': New rotational vector enabling
              to rotate the local spherical coordinate system for
              specification of ray take-off parameters.  New option
              enabling to supplement point sources with the direction
              of the local axis of the spherical coordinate system for
              specification of ray take-off parameters.
            'scronul.for', 'scronum.for', 'scropc.for' and 'scropc.inc'
              replaced by 'scro.for' and 'scro.inc'.  Screen output is
              controlled by new input parameters.
            'crtlew.for': Program to calculate the length of ray
              segments according to the given angular intervals.
                                                     
    5.80 (2004, June):
            'crt.for','crtin.for','ray.for','raycb.for','raycb.inc',
            'trans.for','coef.for','init.for','initc.inc','rpar.for',
            'rp2d.for','writ.for','scro.for','ap.for','pointc.inc',
            'crt2p.for','crtcart.for','gbopt.for':
              HTML links to the paper on C.R.T. added to the source
              codes (the dates of files and subroutines not updated).
            'crt.for': File 'forms.for' is now included to 'crt.for'.
            'ray.for': Comments updated.
            'raycb.for','crtin.for','ray.for','dcrt.inc':
              Error requirements on subroutine CROSS are corrected with
              regards to the rounding errors, new SEP parameter UEBMUL.
            'raycb.for': *** Error in calculating the R.C.C.S. basis
              vector in anisotropic medium corrected. ***
            'init.for': *** A bug in rotation of ray take-off parameters
              fixed. ***
            'rpar.for': *** The bug, disabling multiple ray-parameter
              domains for a single elementary wave, fixed. ***
              Comments updated.
            'rp3d.for': Small bugs in searching for boundary rays fixed.
              A small bug in decision between initial-value ray tracing
              and controlled initial-value ray tracing according
              to the value of AERR fixed. Formats of warnings improved.
            'writ.for','scro.for','scro.inc','ap.for','rpplot.inc',
              'mtt.for','mttgrd.for','wfsrf.for': Comments updated.
            'crtout.for','crtpts.for','crtray.for','green.for': Proper
              source name in subroutine TXT2 used.
            'crtout.for','crtpts.for': Wrong omitting of small
              amplitudes corrected.
            'wan.for': Comments updated.
            *** new ***
            'ray.for','raycb.for','writ.for','writ.inc': New reason
              IEND=39 of the termination of the computation of a ray
              (too small velocity).
            'writ.for','writ.inc','pointc.inc','ap.for','crt2d3d.for',
              'crt2p.for','crtcart.for': Unformatted output files
              of program CRT now contain also the KMAH index and the
              upper error bound for ray tracing.
            'an.for': New file with subroutines to modify the output of
              subroutines of file 'ap.for' in anisotropic media.
              The current version contains subroutine AN03 correcting
              the basis vectors of the intrinsic ray-centred coordinate
              system in anisotropic media.
            'rpplot.for': The program may now display also the results
              of an initial-value ray tracing and of a one-parametric
              shooting.  The reference surface may be parameterized also
               by the third model coordinate.
            'crtout.for','crtpts.for': Complex amplitude may be written
              also as the absolute value and phase.
            'invtt.for': Upgraded from inversion for model parameters
              to simultaneous inversion for hypocentral parameters
              (coordinates and time).
                                                     
    5.90 (2005, June):
            'crtin.for': Comments updated.
            'rpar.for','initc.inc': Comments updated.
            'rp2d.for','rp3d.for','rp3d.inc','writ.for','rpplot.for',
              'crt2d3d.for','mtt.for','wfsrf.for','crt2p.for',
              'crtcart.for','crtlew.for','gbopt.for':
              Comments updated (change of "CRT-?" to "'CRT-?'") without
              change of dates and versions.
            'rp3d.for': Minor correction.
            'writ.for': The bug in determining the source index fixed.
            'writ.for','writ.inc': The maximum number of available
              logical unit numbers increased to 30.
            'ap.for': Indication of a new ray in subroutines AP00, AP02,
              and AP03, failing for multiple sources, fixed.  Minor
              changes in AP03, which should not influence its output.
            'an.for': Comments updated.
            'apvar.for': Error, occuring in subroutine AP29 for rays
              terminating at the boundary of the computational volume,
              corrected.
            'crtout.for': A small bug in writing fixed.
            'rpplot.for': A small bug in a warning generation fixed.
              New SEP parameter CALCOPS for PostScript file setup.
            'mtt.for': Sorting of arrivals at a gridpoint generalized
              (new SEP parameters MTTSORT and MTTORDER).
            'mtt.for','mttq.for': Interpolation of amplitude modified
              for Kirchhoff migration (SEP parameter AMPKI).
            'mtt.for','wfsrf.for','mttgrd.for','crtray.for',
              'crtpts.for','green.for' ... New SEP parameters MINDIG
              and MAXDIG (without change of dates and versions).
            'green.for': Comments updated.
            'wan.for': A bug in second-order perturbations along
              isotropic rays fixed.
            *** new ***
            'ap.for': New subroutine APYYF to mutually exchange values
              stored in arrays Y and YF. May be used, e.g., when calling
              subroutine AP03 for a point O/F stored in YF.
            'rpplot.for': Elementary wave to be plotted may be selected
              also according to the index of the source.  Default value
              of parameter IWAVES changed, but the change should not
              affect almost any existing computation.
            'green.for','wan.for': The second-order travel-time
              perturbations from anisotropic common rays
              to anisotropic-ray-theory rays and to isotropic common
              rays can be calculated along anisotropic common rays.
            'watable.for': Program for calculation of differences
              between travel times and their approximations
              by the second order perturbations.
                                                     
    6.00 (2006, June):
            'crtin.for': Comments updated.
            'init.for': *** Error in initial slowness vector in
              subroutine INIT2 fixed. ***
            'init.for','mttq.for','mttgrd.for','crtout.for',
              'greenss.for','gbopt.for':  Undefined value UNDEF is now
              determined by function UARRAY of file 'forms.for'.
            'rpar.for': Unit-sphere metric tensor for a point or line
              source corrected. Check on positivity of ANUM and BNUM for
              two-parametric ray tracing added.
            'crtcart.for': Minor changes due to the new non-Cartesian
              coordinate systems in file MODEL.
              Minor changes in the screen output.
            'green.for': New check for a point source.
            'crtout.for','crtpts.for','wan.for': Comments updated.
                                                     
    6.10 (2007, June):
            'rpar.for','rpard.inc': Comments updated.
            'crt.htm': Comments updated.
            'mtt.for': Error in subroutine CIQUAR fixed. Comments
              updated.
            'mtt.for','wfsrf.for': Subroutine INDEXX replaced by INDEXI.
            'mtt.for','mttgrd.for': New SEP parameter NUMLIN
              (no change in file dates).
            'invtt.for': Modified to conform to the new programs
              for matrix operations.
            'gbopt.for': Moved to packaga DATA, directory MAR.
            *** new ***
            'codes.dat': New file CODE to specify refracted S wave.
                                                     
    6.20 (2008, June):
            'rpar.for': Minor error in writing to the output log file
              fixed.
            'ap.for': Unnecessary declarations in subroutine APYYF
              removed.
            'mtt.for','mttq.for','mtt.inc','wfsrf.for','mttwf.inc':
              New quantities which may be interpolated between rays
              or recorded along wavefronts. Files with quantities
              specified on the ray-parameter grid may now contain
              undefined values in the gridpoints not used during
              interpolation.
            'mttq.for': A bug in calculation of GBW22 and GBW2
              corrected, comments updated.
            'greenss.for': Comments updated.
            'crtout.for': Comments updated.
            'invtt.for': Modified to conform to the new versions of
               subroutines of file 'mat.for'. Format 'G' changed to 'E'.
            Attribute TYPE="..." added into all HTML links
              to text/html or text/plain files with extension other
              than .htm (without date or version change).
            *** new ***
            'crt.for','crtin.for','rpar.for','writ.for': New input SEP
              parameters RPAREW and WRITEW which enable repeated use
              of the input data RPAR-(4) and WRIT-(6).
            'init.for','initd.inc': Coordinates of point sources
              specified in file SRC are read sequentially.
            'mtt.for': Interpolation to the individual points coded.
            'green.for': Green functions for multiple point sources
              specified in file SRC may be calculated.  Green functions
              in the output file may be sorted according to the
              different sorting criteria.
                                                     
    6.30 (2009, June):
            E-mail addresses replaced by WWW addresses
              (without date or version change).
                                                     
    6.40 (2010, June):
            'ap.for','mttq.for': Dealing with infinite amplitudes
              corrected.
            'crtpts.for': Comments updated (no date or version change).
            'rp3d.for': Wrong dealing with parameter PRM0(2) corrected.
            'mtt.for': Exceptional appearence of too small interval
              for solving the cubic equation removed. Comments updated.
            'mtt.for','wfsrf.for': Comments updated.
                                                     
    6.50 (2011, May):
            'green.for': Description of input parameter MODEL updated.
            'greenss.for': Comments updated, variables renamed.
            'crtlew.for','mtt.for': Indentation of comments corrected.
            'code.for': Comments updated.
            'mtt.for': Small bug causing unnecessary appearence
              of warning MTT-30 fixed. A bug causing error MTT-08 fixed.
            'wan.for': Array dimension MNEWP extended, memory management
              of arrays KNEWP, RNEWP improved.
            'rpplot.for': New parameter SHOWPAGE useful to disable
              the PostScript 'showpage' command.
            'rpar.for': Comments corrected.
            *** new ***
            'init.for','writ.for': Writing of initial points of non
              existing rays to file CRT-I coded.
                                                     
    6.60 (2012, June):
            'code.for': Comments updated.
            'coef.for': A bug in calculation of R/T coefficients fixed.
            'green.for','wan.for': Output of the values of eigenvectors
              to an optional output file coded.
            'greenss.for': New parameter GSEWIDTH to control the width
              of the output field reserved for one integer value of
              the seismogram.
            'invtt.for': Comments updated.
            'mtt.for': Description of input SEP parameters improved.
            'mttgrd.for': Description of input data updated.
            'wan.for': Calculation of angular rotation of eigenvectors
              corrected.  Normalization of vectors in subroutine for
              vector projection added.
              Comments updated.
            *** new ***
            'green.for','wan.for': Prevailing-frequency approximation
              of the coupling ray theory coded.
                                                     
    7.00 (2013, June):
            'crtin.for': New check whether the input files are
              specified. The description of the azimuthal equidistant
              projection (under the description of INIPAR) corrected.
            'raycb.for': Integer function KOOR in RAYCB, and V2 in FCTA
              declared. Considerably improved description.
            'rpar.for': Integer function LUWARN in RPAR2 and SRPARH,
              and SCALE in RPAR4 declared.
            'ray.for','pointc.inc': Considerably improved description.
            'ap.for': Subroutine APYYF corrected. Description updated.
            'an.for': Updated to comply with the new version of
              'hder.for' from package MODEL.
            'crt2d3d.for','crt2p.for': *** Programs out of order since
              version 5.50 corrected. ***
            'mttq.for': *** Wrong projection of the P-wave polarization
              vector onto the basis vector of the ray-centred coordinate
              system in the case of an anisotropic model corrected. ***
              A bug in reading of the names of interpolated coordinates
              of the initial points of rays fixed.
            'green.for': Wrong number of error GREEN-09 corrected,
              the message of error GREEN-08 corrected, description of
              input parameters updated. Possibility of wrong projection
              of the P-wave polarization vector onto the basis vector of
              the ray-centred coordinate system in the case of an
              anisotropic model corrected. Comments updated.
            'wan.for': *** Two errors in calculation of the propagator
              matrix for prevailing frequency approximation corrected.
              Error in calculation of DEFI for prevailing frequency
              approximation corrected. ***
              Description of error WAN-03 corrected. Missing declaration
              of subroutines HDER and VELOC added. Updated to comply
              with the new version of 'hder.for' from package MODEL.
              Comments updated.
            'rpplot.for': Error message updated.
            'wanpfa.for','wan.for': Original file 'wan.for' has been
              split into two new files 'wanpfa.for' and 'wan.for'.  File
              'wanpfa.for' now contains subroutines called from both
              'wan.for' and 'crtpfa.for'.
            'mtt.for','mttq.for','rp3d.for','rpplot.for','rpsymb.for',
              'watable.for','wfsrf.for': Comments updated.
            *** new ***
            'apw.for': New subroutines to write the quantities at the
              points of rays into unformatted output files.
              The quantities are stored in common block /POINTC/
              defined in file 'pointc.inc'.
            'crt.for','writ.for','writ.inc','crt2d3d.for','crt2p.for',
              'crtcart.for': Writing the quantities at the points of
              rays into unformatted output files has been unified using
              the subroutines of file 'apw.for'.
            'ray.for','raycb.for','raycb.inc','init.for','initc.inc',
              'writ.for','pointc.inc','ap.for','mtt.for','mttq.for',
              'green.for','wan.for': Reference polarization vectors
              introduced (basis vectors of the ray-centred coordinate
              system were incorrectly substituted in the previous
              versions).
            'mtt.for': Option to choose between bilinear and bicubic
              interpolation of travel time added.
            'crtpfa.for','crtpfa.inc': New program CRTPFA to calculate
              two prevailing-frequency coupling-ray-theory S-wave Green
              tensors along each input reference ray, to double the
              input reference rays, and to write the first of the
              doubled rays with the first Green tensor, and the second
              of the doubled rays with the second Green tensor.
            'pfatubes.for','pfatubes.inc': New program PFATUBES to
              modify the file 'CRT-T' with indices of triangles in order
              to enable interpolation within ray tubes formed by rays
              written by program CRTPFA.
                                                     
    7.10 (2014, June):
            'crt.htm': Compiling instructions updated.
            'green.for': *** Serious error in writing the output
              formatted file with the Green tensor without sorting
              according to receivers has been fixed. ***
            'init.for': Declaration of dummy variable DUMMY improved.
            'pfatubes.for': Comments updated.
            'ray.for': Comments considerably updated.
            'raycb.for': Error in storing the spatial gradient of the
              Hamiltonian function at surfaces in anisotropic media
              fixed. Missing initialization of parameter CRTANI in
              subroutine CDEF added. Missing initialization of ISHIFT
              in the initial point of the ray added.  Comments updated.
              Description of subroutine PVINT added.
            'rpar.for': *** Error in subroutine IHIST fixed. ***
              Minor update of the dimension of array IY.
            'trans.for': Reason of termination IEND=37 renamed to 27,
              minor update of the dimension of array IY, comments
              updated.
            'wfsrf.for','wfsrf.inc': Minor bug in declaration of
              character variables removed.
            'wan.for','crtpfa.for','crtpfa.inc': "Single-frequency"
              changed to "prevailing-frequency".
            *** new ***
            'rpar.for','crtin.for': New SEP parameter KMAHI enabling to
              exclude the KMAH index from the ray history.
            'rpplot.for','rpplot.inc': Plotting of symbols and numbers
              corresponding to the plotted ray histories under the
              horizontal axis of the figure coded.
            'an.for','crtin.for','crtpfa.for','init.for','pointc.inc',
              'ray.for','raycb.for','trans.for','wan.for','writ.for',
              'writ.inc':
              New possibility to trace anisotropic-ray-theory S-wave
              rays instead of common S-wave rays using new version of
              hder.for from package MODEL. New SEP parameter KSWAVE.
              New SEP parameter DSWAVE describing the minimum difference
              between the eigenvalues of the S waves. New reasons
              IEND=38 and 75 of termination of ray tracing.