Released versions of package MODEL
                                                                   
                                                     
    1.00 (1988, June):  Preliminary version, contains only subroutines
            for model specification.  There are no complete ray
            tracing subroutines yet.
                                                     
    2.00 (1990, February):  Common release with complete ray tracing
            routines.  First consistent version of the ray tracing
            program.  Complete ray tracing poorly debugged.
                                                     
    3.00 (1991, January):  Common release with complete ray tracing
            routines.  Principal errors removed from complete ray
            tracing.
            'parm.for': Evaluation of S-wave quality factor corrected.
                                                     
    4.00 (1992, December):  MODEL and CRT packages have been
            split: 'raycb.for' split into 'means.for' (MODEL) and
            'raycb.for' (CRT).  Subroutine FPOWER moved from 'val.for'
            to 'model.for'.
            'val.for': Incorrect storage of function coefficients in
              common block /VALC/ fixed.  New check for incorrect
              indices of the class or group during invocation of VAL2.
              Bugs in the evaluation of embedded functions fixed.
            'val.for': Incorrectly coded linear extrapolation of
              functions outside the given spline grid replaced by
              analytic continuation.  Linear version partially fixed
              and denoted with 'CV3' in the first three columns.
            'val.for': Hermite representation of 1-D cubic splines
              replaced by a B-spline representation (CURVB1 and CURVB2
              of 'fit.for' called instead of CURVN1 and CURV2D).
            'model.for', 'srfc.for', 'parm.for', 'val.for', and
              'fit.for': Minor corrections to conform with the
              FORTRAN77 standard.
            'means.for': *** Considerable changes and corrections.***
            *** new ***:
            'model.for', 'parm.for', 'val.for', and 'fit.for':
              Invocations of VAR* routines enabling inversion have
              been added and denoted by 'V' in the first column.
            'var.for', 'varnul.for', and 'spsp.for':  New additional
              model specification subroutine files for inverse
              modelling.
            'grid.for', 'modsec.for', 'sec.for', 'secdxf.for', and
              'secacd.for': New sample application programs and
              routines working with the model, mostly for the purposes
              of model displaying.  For the same reasons, subroutine
              CARTES has been added to 'metric.for'.
            'clean.for': New simple program to enable a conditional
              compilation.
                                                     
    4.10 (1994, January):
            'model.for', 'parm.for', 'val.for', 'var.for',
            'varnul.for', 'means.for', 'grid.for', 'modsec.for',
            'lindxf.for', 'clean.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).
            'model.for', 'metric.for', 'val.for', 'modsec.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.
            'spsp.for': External procedures declared external.
            'modsec.for': Two severe bugs fixed (index of a simple
              block, section boundaries).
            'model.for', 'means.for', 'grid.for', 'modsec.for',
              'clean.for':  Other minor fix-ups and improvements.
            *** new ***:
            'forms.doc': General description of files containing Lines
              (lines at interfaces, velocity isolines, rays, etc.) or
              Points (gridded interfaces, sources, receivers, ray
              endpoints, etc.).  The files are introduced especially
              to simplify data transfer and plotting.
            'grid.for': Model specified in curvilinear coordinates is
              now gridded in Cartesian coordinates.
            'array.for': New subroutines to write real arrays into
              disk files and to read them.  Common with package 'NET'.
            'modsec.for': New option of generating regularly spaced
              points along structural interfaces or velocity isolines.
              New format of output files is described in 'forms.doc'.
              Common specification of parallel profiles - a change in
              the input data for the profiles (obligatory slash).
            'lindxf.for', 'linacd.for': Replaced 'secdxf.for' and
              'secacd.for' to transform lines into the CAD or ACROSPIN
              format.
                                                     
    5.00 (1996, September):
            'model.for', 'parm.for', 'val.for', and 'fit.for':
              Invocations of VAR* routines enabling inversion are
              denoted by '*V' instead of 'V ' in the first two
              columns.  No need to patch the code before compilation
              henceforth.
            'model.for': *** Change in input data for model ***
              (IVERT key added).  Subroutine BLOCK slightly extended.
            'metric.for': Subroutine CARTES corrected.
            'val.for': *** Input grid values for interpolation may now
              correspond to any power of the interpolated quantity.
              Model data read by 'srfc.for' and 'parm.for' changed.***
              Default keys defining the function form introduced.
              Number of model parameters increased to NPAR=100000.
            'var.for': Number of registers and variations increased to
              MFUNCT=48 and MB=3072.
            'means.for': *** Considerable changes and corrections.***
              Unfortunately, not finished.
            'grid.for':  *** Change in input data, in generation of
              the partial derivatives, etc. ***
            'array.for': Renamed to 'forms.for', updated, supplemented
              with subroutines FORM1 and FORM2.
            'sec.for'+'modsec.for': Joined to single file 'sec.for'.
              Considerably updated.
            'clean.for': Updated.
            'mod.bat': *** Considerably changed.***
            'lindxf.for', 'linacd.for': Removed (moved to package D3).
            'calcomp.for': Moved from package CRT.
            *** 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.
            'parm.for': Extended to anisotropic models with
              attenuation, maintaining all compatibility with the
              isotropic models.
            'modelv.for','parmv.for','valv.for','fitv.for': Versions
              of 'model.for', 'parm.for', 'val.for', and 'fit.for' for
              inverse problems.
            'length.for': Simple subroutine to determine the length of
              a string.
            'gse.for': Subroutines to write and read seismograms in
              the GSE data exchange format.
            'calcops.for': CalComp to PostScript graphics interface.
            'modchk.for': Program to check the model consistency.
            'intf.for': Program to check the positions of given
              points with respect to interfaces in the model.
            'srp.for': Program to generate source and receiver points
              corresponding to given configuration parameters.
            'pallet.for': Program to interpolate the RGB colour pallet
              linearly in the HSB colour space.
            'sd','slit','wb','l7','mar': Subdirectories with examples
              of input data for seismic models.
                                                     
    5.10 (1997, October):
            *** probably not all changes are listed here ***
            'forms.doc','length.for','forms.for','gse.for','srp.for',
              'calcomp.for','calcomp.inc','calcops.for','calcops.inc',
              'pallet.for','f': Moved to new package FORMS
              ('forms.doc' renamed to 'formsdoc.htm').
            'indexx.for': Moved to new package NR.
            'soft.for','inv1soft.for','inv3.for','inv4.for','inv3.dat':
              Moved from package CRT.
            'soft.for': *** Severe bug fixed. ***
            'model.doc' renamed to 'modeldoc.htm'.
            'lmod.bat' renamed to 'fmod.bat' and revised.
            'gridnet.dat' renamed to 'grid.h' and changed into SEP.
            'model.for','modelv.for','metric.for','sec.for':
              BLOCK DATA subprograms canceled.
            'modchk.for','grid.for','inv1soft.for','inv3.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.
            *** new ***
            All Fortran files supplemented with HTML references.
            'grid.for': Grid dimensions specified by SEP parameter
              file.
            'len-grd.bat'... MS-DOS batch file to display 2-D velocity
              sections across the demo model 'model.dat'.
                                                     
    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('...').
            'modeldoc.htm' split into 'modeldoc.htm' and 'modelver.htm',
              list of files moved to 'model.htm'.
            'parm.for': Bugs disabling anisotropic models fixed.
              New entry PARM4 determining whether a model is isotropic.
            'modchk.for': Undefined free-space simple blocks now may or
              may not be reported.
            'grid.for': *** Input data changed. ***
            'grid.h': Updated.
            *** 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.
                                                     
    5.30 (1999, June):
            'model.for': Fatal bug in subroutine FPOWER when calculating
              the power of a zero material parameter fixed.  Subroutine
              BLOCK completely rewritten and its extended version BLOCKS
              added.  Subroutine INTERF upgraded, new subroutine SEPAR
              supplemented.
            'means.for', 'grid.for', 'sec.for': Updated to correspond to
              the new version of subroutines BLOCK and BLOCKS.
            'val.for': Zero POWERW in input data now reported as error.
            'model.dat', 'prem/prem-mod.dat', 'elf1/elf1-mod.dat',
              'wb/wb2-mod.dat','l7/l7-mod.dat': Free space simple blocks
              added.
            *** new ***
            'modsrf.for', 'modsrf.inc': Program to approximate
              structural interfaces and velocity sections by polygons.
            'bndlin.for': Program to write edges of the model box.
            'len-mod.h', 'elf1/elf1-mod.h', 'sd/sd1-mod.h',
              'sd/sd2-mod.h', 'wb/wb2-mod.h', 'l7/l7-mod.h' and
              corresponding data '*/*-cam.dat' and '*/*-dli*.dat':
              History file to generate 3-D VRML97 representations of
              structural interfaces and velocity distribution in the
              respective models. '*/*-cam.dat' describe the
              corresponding initial positions of the camera and
              '*/*-dli.dat' the directional lights.
            'wrl': Subdirectory with 3-D VRML97 representations of
              several 3-D models.
                                                     
    5.40 (2000, May):
            'modchk.for', 'sec.for', 'intf.for':
              *** Input data changed to SEP format. ***
            'grid.for':
              *** Input data changed. ***
              Multiple files from * device moved to the history file.
            'model.htm': Considerably revised.
            'modeldoc.htm' discarded (information moved to 'model.htm').
            'model.for', 'model.inc': Now reading parameter NEGPAR.
            'parm.for': Check for negative material parameters may now
              be disabled by SEP parameter NEGPAR, see 'model.for'.
            'val.for': Missing initialization of variable GROUP fixed.
            'val.inc': Comments updated.
            'soft.for': *** Different weights for different material
              parameters introduced.  Incorrect ordering of independent
              variables (coordinates) fixed.  Two additional severe bugs
              related to array indices in common block VALC fixed. ***
            'modchk.for', 'sec.for', 'intf.for': Since 'model.for' is
              reading NEGPAR, 'sep.for' has been included.
            'bndlin.for': Minor bugs fixed.
            'modsrf.for': Input parameters COLUMNii, POWERii, IVALUEii
              extended by ii=01,02,...,06.  New option COLUMNii='SRF'
              introduced.  Some bugs fixed.
            'grid.for':
              *** Discretization of all material parameters and of
              functions describing interfaces enabled. ***
              'model.inc' included because of parameter NEGPAR.
              Grid may be specified in Cartesian or model coordinates.
            'sec.for':
              Output format corrected.
            'inv3.for' discarded (replaced by better program
              'modmod.for').
            'inv4.for' discarded, because 'modmod.for' followed by
              'grid.for' and 'grdcal.for' do a better job.
            'gels.for': Moved to package FORMS.
            Subdirectories with the data for particular models moved to
              new package DATA.
            'len-*.*' moved to subdirectory 'len' of package DATA.
            'model.dat' renamed to 'len-mod.dat', 'grid.h' to
              'len-grid.h', 'sec.dat' to 'len-sec.dat', 'sec-pts.dat' to
              'len-secp.dat' and all moved to subdirectory 'len' of
              package DATA.
            'soft.dat' replaced with 'sob11.dat'.
            'grid.dat' and 'inv3.dat' deleted because are used no more.
            *** new ***
            'inv1soft.for' renamed to 'invsoft.for' and considerably
              updated (different weights of Sobolev scalar products for
              surfaces and various material parameters, SEP format of
              main input data, output in the form of vectors and
              matrices for convenient processing).
            'invpts.for: Program to calculate the derivatives of
              functions, describing interfaces or material parameters,
              with respect to the model B-spline coefficients.
            'modmod.for': New program to modify the model (update or
              change parametrization).
            'modle2d.for': Provisional version of the program to
              calculate directional Lyapunov exponents and average
              Lyapunov exponent for a 2-D model without interfaces.
            'sob22.dat','sob22n.dat','sob22l.dat','sob33.dat',
              'sob33n.dat','sob22l.dat': General specifications of
              isotropic Sobolev scalar products.
                                                     
    5.50 (2001, June):
            'metric.for': *** Wrong Christoffel symbols in geographic
              spherical coordinates fixed. ***
            'soft.for': Changed to treat surfaces and material
              parameters separately.
            'modchk.for': Comments updated.
            'modsrf.for': *** Functionality considerably improved: ***
              Identification of intersections of gridlegs
              with interfaces improved.  Identification of intersections
              of gridfaces with edges on interfaces improved.
              New algorithm for creation of polygons from the identified
              intersection points coded.
            'grid.for': *** Wrong gridding of oblique vertical sections
              fixed. ***  Comments corrected.
            'intf.for': Changed to enable writing of results to other
              than first four columns of the output file, and to enable
              preserving the values from input file.
              *** For special case KOLUMN=0 and KSRFC=0 input data changed
              to KOLUMN=-1 and KSRFC=0. ***
            'invsoft.for': *** Wrong output values of model parameters
              fixed.  Check of the dimension of array RAM improved. ***
            'invsoft.for', 'invpts.for': *** New input parameter ICLASS,
              enabling to separate inversions of surfaces and material
              parameters. ***
            'invsoft.for', 'invpts.for', 'modmod.for': *** Revised
              to understand new parameters FORMM, FORMMR and FORMMW,
              included to switch the form of the files with matrices
              between formatted and unformatted. ***
            'modle2d.for': *** New parameter NY, enabling to perform
              calculations also in 3-D models.  Models with free space
              enabled. ***  Output format updated.
                                                     
    5.60 (2002, May):
            'modsrf.for': Comments updated, minor change to decrease
              the error in the position of structural edges.
            'modmod.for': *** Poor declaration of external function
              LENGTH fixed. ***
                                                     
    5.70 (2003, May):
            'modle2d.for': Weighting of the directional Lyapunov
              exponents and of the mean Lyapunov exponent coded.
              Poor declaration improved.
            *** new ***
            'hder.for': Subroutines to calculate the phase-space
              derivatives of the Hamiltonian in anisotropic media.
            'coorchg.for': Program to transform the coordinates of lines
              or points from Cartesian coordinates to polar spherical or
              geographic spherical coordinates and vice versa.
                                                     
    5.80 (2004, May):
            'model.for': Check of the size of model coordinates with
              respect to the model dimensions.
            'means.for': Comments updated.
            'modsrf.for': The default value of ERRSRF accounts for the
              absolut value of coordinates, not only of gridsteps.
              Comments updated, numbers of error messages updated.
            'grid.for','srfc.for','invsoft.for','invpts.for':
              Comments updated.
            *** new ***
            'well.for': A new subroutine to extract a 1-D vertical
              profile from the given model.
            'modchk.for': Logical test for overlapping simple blocks
              coded.
            'invsoft.for': Upgraded from inversion for model parameters
              to simultaneous inversion for hypocentral parameters
              (coordinates and time).
            'srcsrc.for': New program designed to update the source
              coordinates during the simultaneous inversion of arrival
              times.
                                                     
    5.90 (2005, June):
            'model.for': Comments updated.
            'hder.for': Comments updated.
            'modsrf.for','grid.for','intf.for','coorchg.for',
              'modmod.for': New SEP parameters MINDIG and MAXDIG
              (without change of dates and versions).
                                                     
    6.00 (2006, June):
            'parm.for': *** In subroutine PARM2, the default isotropic
              reference material corresponding to given anisotropic
              material was wrong.  In subroutine PARM3, the default
              anisotropic elastic moduli corresponding to given
              isotropic reference material were wrong if both P- and
              S-wave velocities were specified. ***
            'model.for','metric.for','metric.inc': *** Two new spherical
              coordinate systems added. ***
            'intf.for','coorchg.for','invpts.for':  Undefined value
              UNDEF is now determined by function UARRAY of file
              'forms.for'.
            'coorchg.for': The non-Cartesian coordinate system is now
              specified by parameter MODEL instead of parameter KOOR.
              Minor changes in the screen output.
            'invpts.for': A bug, serious but appearing only if POWER
              differs from POWERM, fixed.  Comments extensively updated.
              Negative values of D1, D2 and D3 enabled.
            'means.for','modsrf.for': Comments updated.
                                                     
    6.10 (2007, June):
            'model.htm': Comments updated.
            'invsoft.for,'invpts.for','modmod.for': Modified to conform
              to the new programs for matrix operations.
            'modmod.for','grid.for': New SEP parameter NUMLIN (no change
              in file date).
                                                     
    6.20 (2008, June):
            'bndlin.for','sec.for': Format 'G12.6' changed to 'G13.6'.
            'grid.for': New parameter to control screen output.
            'invsoft.for,'invpts.for','modmod.for': Modified to conform
              to the new versions of subroutines of file 'mat.for'.
            Attribute TYPE="..." added into all HTML links
              to text/html or text/plain files with extension other
              than .htm (without date or version change).
                                                     
    6.30 (2009, June):
            E-mail addresses replaced by WWW addresses
              (without date or version change).
            'val.for': Comments updated.
                                                     
    6.31 (2009, June):
            'val.inc': Comments updated.
                                                     
    6.50 (2011, May):
            'grid.for': Subroutine WARRAI used for writing to the output
              file with indices of complex blocks.
            'modmod.for': Comments updated.
            'invpts.for': Error message modified.
            'clean.for': Modified to enable the length of comment lines
              up to 254 characters.
                                                     
    6.60 (2012, June):
            'grid.for': Description of parameter NEGPAR added.
            'modchk.for': Messages to the output file modified.
                                                     
    7.00 (2013, June):
            'modsrf.for','coorchg.for': Comments updated.
            *** new ***
            'hder.for': Subroutine HDER now returns also the
              eigenvectors of the Christoffel matrix.
                                                     
    7.10 (2014, June):
            'hder.for': Comments updated.
            'modchk.for': Minor change of output message.
            'model.for': Minor change - declaration improved.
            'model.htm': Compiling instructions updated.
            'parm.for': ***Serious bug in subroutine PARM4 corrected.***
            *** new ***
            'hder.for': New option to calculate the anisotropic-ray-
              theory S-wave Hamiltonian functions required to trace
              anisotropic-ray-theory S-wave rays coded (new parameter
              KSWAVE).  New parameter DSWAVE specifying the minimum
              relative difference between the eigenvalues of the S
              waves.
                                                     
    7.20 (2015, June):
            *** new ***
            'hder.for': New option to calculate the anisotropic-ray-
              theory SH-wave and SV-wave Hamiltonian functions required
              to trace anisotropic-ray-theory SH-wave and SV-wave rays
              in approximately transversely isotropic medium coded
              (new parameters TIA1,TIA2,TIA3).
            'hdertest.for','hdertest.h','hdertest.dat': New program
              HDERTEST to test the calculation of the first-order and
              second-order spatial derivatives of the Hamiltonian
              function. Example of history file and data file.
                                                     
    7.40 (2017, June):
            'invsoft.for': Error messages updated.
            'coorchg.for','grid.for','intf.for','invpts.for',
              'modmod.for': Value of UNDEF used for undefined real
              values may now be specified as input SEP parameter (with
              date and version change).
                                                     
    7.50 (2018, December):
            'hder.for','hdertest.for','hdertest.h','hdertest.dat':
              Subroutine file and program moved to package FORMS.