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.