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Description of the program  V E L P L
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     Program VELPL is designed for plotting plane sections of
slowness, phase velocity and group velocity surfaces in an arbitrary
anisotropic medium. File LU3 generated in the program ANRAY contains 
data for the plots.

                                                     
Description of input and output files
-------------------------------------
    Main input data are read from the standard input by list-directed
input (free format) and consist of a single line containing following
data:
    'LIN' 'LOU' 'LU3'/
Here:
    'LIN' is the name of the input data file LIN.
    'LOU' is the name of the output log file LOU.
    'LU3' is the name of the input data file LU3,
          generated by program ANRAY.
    / is a slash recomended in batch and script files to enable future
        extensions.
Defaults:
    'LIN'='velpl.dat'
    'LOU'='velpl.out'
    'LU3'='lu3.dat'
Example of the main input data:
    'velpl.vel' /

    Input data consist partially of the data obtained in the program
ANRAY, which are stored in the formated form in the file LU3, 
and partially of the additional input data read by list-directed 
input (free format), specified by the user in the file LIN. Output data
describing the computations are stored in the file LOU. The program  
generates a postscript file with the desired plot.

                                                      
Description of the content of the file LU3
-----------------------------------------

    File LU3 contains data necessary for construction of sections of
slowness surfaces, phase velocity and group velocity surfaces 
generated in the program ANRAY. The data are stored in LU3 in the 
following formatted form:

1) ITYPE,NPAR,INUM                               FORMAT(16I5)

      ITYPE...  ITYPE=1: qS1 wave.
                ITYPE=2: qS2 wave.
                ITYPE=3: qP wave.

      NPAR...   NPAR=1: plot of section of slowness surface.
                NPAR=2: plot of section of phase velocity surface.
                NPAR=3: plot of section of group velocity surface.

      INUM...   number of samples in the plot.

2) DDELTA,XX(I),YY(I),ZZ(I)                       FORMAT(4E15.5)

      DDELTA... angle (in radians), for which the vector (XX,YY,ZZ)
                is calculated.

      XX(I),YY(I),ZZ(I)... x,y and z components of the slowness vector
                (if NPAR=1), phase velocity vector (if NPAR=2) or
                group velocity vector (if NPAR=3) for the angle
                DDELTA. Maximum points: 300.

   The line 2 is repeated for all the angles of all the three waves.


                                                      
The additional input data in the file LIN
-----------------------------------------

     These data are specified by the user. They control plotting.

1) TEXT

   Arbitrary alphanumerical text which is shown below the plots.
   Default 'VELPL'.

2) IPLOT,IPRINT,SC,PSTEXT

    IPLOT...    controls the form of the resulting plot.
                IPLOT.GE.0: polar plot of a section of a surface.
                IPLOT.LT.0: plot of one quadrant of a section of
                a surface in a rectangular frame (horizontal axis:
                angle (in degrees); vertical axis: velocity (slowness).

    IPRINT...   controls the printout into the file LOU and the type
                of the name of the postscript file with a plot.
                IPRINT.GE.0... automatic generation of postscript file
                names: plot00.ps, plot01.ps, etc.
                IPRINT.LT.0... postscript file name specified by the user,
                see PSTEXT.
                IPRINT=0... print of input data only (default value).
                IABS(IPR)=1... print of velocity (slowness) vectors
                for each specified angle.

    SC...       scaling factor, controls the scales of tics and
                alphanumeric texts. For SC=1., the tics are 0.15 
                cm long and coordinates and text describing the 
                plot are 0.4 and 0.45 cm high, respectively.
                Deafult SC=1.

    PSTEXT...   the name of the postscript file specified by the user;
                it is used only if IPRINT.LT.0.

3) If IPLOT.GE.0, then: XM,XLEN,DTICX,YM,YLEN,DTICY

    XM...       horizontal halflength of the frame, in which the
                section of a surface is to be displayed, in user 
                length units, e.g. km.

    XLEN...     length of the horizontal axis, in cm.

    DTICX...    the distance between two neighbouring tics on the
                horizontal axis. The tics are denoted by the 
                corresponding coordinate values (in the user length 
                units).
                DTICX.GT.0.: Tic marks starting from -XM and
                appearing at the subsequent points -XM+DTICX,
                -XM+2.0*DTICX,...
                DTICX.LT.0.: Tic marks start and continue to be
                plotted from the first integer multiple of
                ABS(DTICX) greater than -XM.

    YM,YLEN,DTICY... the same for the vertical axis.

   If IPLOT.LT.0, then: XLEN,DTICX,YMIN,YMAX,YLEN,DTICY

    XLEN...     length of the horizontal axis, in cm.

    DTICX...    the distance between two neighbouring tics on the
                horizontal axis. The tics are denoted by the 
                corresponding coordinate values (in the user length 
                units).
                DTICX.GT.0.: Tic marks starting from 0. and
                appearing at the subsequent points DTICX,
                2.0*DTICX,...
                DTICX.LT.0.: Tic marks start and continue to be
                plotted from the first integer multiple of
                ABS(DTICX) greater than 0..

    YMIN,YMAX... the minimum and maximum values along the vertical axis 
                (in velocity (slowness) units). 

    YLEN...     length of the vertical axis, in cm.

    DTICY...    the distance between two neighbouring tics on the
                vertical axis. The tics are denoted by the 
                corresponding coordinate values (in velocity
                (slowness) units).
                DTICY.GT.0.: Tic marks starting from YMIN and
                appearing at the subsequent points YMIN+DTICY,
                YMIN+2.0*DTICY,...
                DTICY.LT.0.: Tic marks start and continue to be
                plotted from the first integer multiple of
                ABS(DTICY) greater than YMIN.

4) NTICX,NTICY,NDX,NDY

    NTICX...    the number of marked intervals on the horizontal 
                axis between two neighbouring tics with corresponding 
                coordinate values. Default NTICX=1.

    NTICY...    the same as NTICX, but for the vertical axis.
                Default NTICY=1.

    NDX,NDY,... control the precision of numbers describing the coordinate 
                axes in the plots. NDX corresponds to the horizontal
                axis, NDY to vertical axis.
                ND.GT.0: The number of digits to the right of the
                decimal point.
                ND=0: Only integer portions of the numbers with
                decimal points. Default value
                ND.LT.0:  Integers.

Example of data LIN

Termination of computations
---------------------------

   The computation terminates when the sections of the three waves
propagating in an anisotropic medium are plotted.

                                                      
Output to the file LOU
----------------------
   The file contains a copy of the input data followed by lines
containing the following information: DDELTA,V,XV,YV,ZV.
   DDELTA...  the angle (in radians), for which are the following
              values calculated.
   V...       value of the slowness (NPAR=1), phase velocity (NPAR=2)
              or group velocity (NPAR=3).
   XV,YV,ZV... components of the slowness vector, phase velocity
              or group velocity vector.