**CIGAL Reference Manual, Chapter 4 (Variables): vdata**
===== vdata -- Matrix of lengths and areas computed by SKETCH command =====
**        usage: vdata**
          VDATA is an internally defined matrix variable.  It is created by the SKETCH
      command to store length and area values computed by the MEASURE function.
      The matrix has two real (i.e., floating point) values in each row, length
      first and then area.  The number of rows is determined by how many measurements
      you have made.  Because VDATA is created as a variable in a temporary disk file
      there is no limit to the number of entries you can store (up to the total free
      space on your disk).
      Each time you do a measurement in SKETCH, the values are added to the end of
      VDATA.  If you go in and out of the SKETCH command the matrix does not start over,
      new values just keep adding on at the end.  If you want to erase the values in
      VDATA and start again you use the ERASE command as:
                  erase vdata
  This does not delete the variable, it simply resets its pointers to empty.
      Outside of SKETCH, VDATA can be manipulated just as any other matrix variable.
      For example, you can select values, calculate means, or write the values to a
       disk file or printer.  Because VDATA is stored in a temporary file you should be
       sure to copy it to some other file if you want to save the data beyond the end of
       the current CIGAL session.    The length of VDATA is indicated by the internally
       defined integer variable NVDATA, which is set to the number of rows in the matrix.
       You can change the length of VDATA by changing the value of NVDATA.  For example,
       setting NVDATA to zero is equivalent to erasing VDATA.  You can sometimes also
       recover lost values in VDATA simply by setting NVDATA to the number of rows that
       you used to have, provided that those values have not been overwritten by new values.
      The temporary disk file used to store VDATA (called VDATA.TMP) is not deleted at
      the end of a CIGAL session.  The file will normally be truncated automatically
      during the next CIGAL session when you use the SKETCH command to create VDATA again.
      However if you assign a value to NVDATA, before using the SKETCH command, then the
      VDATA variable is created without truncating the VDATA.TMP file.  This can be used
      to recover VDATA values lost if you exit CIGAL prematurely or after a power failure, etc.
      Examples of using VDATA:
         sketch                           ; draw vectors and measure many
                                          ; lengths and areas
         type vdata                       ; type out values on screen
         mean(vdata(0))                   ; calculate mean of lengths
         a = mean(vdata(1))               ; store mean area in variable A
         type vdata(0) > 'leng.dat'       ; store lengths in file
         type vdata(1,3:20) > 'area.dat'  ; store some areas in file
         type vdata > 'all.dat'           ; store length and areas in file
         erase vdata                      ; reset VDATA variable to empty
  
   [ERASE][2].
**See Also:**\\
[[jvs:cigal:manual:chapter2:erase|ERASE(2)]], 
[[jvs:cigal:manual:chapter4:nvdata|NVDATA(4)]], 
[[jvs:cigal:manual:chapter2:sketch|SKETCH(2)]], 
[[jvs:cigal:manual:chapter1:variables|VARIABLES(1)]], 
[[jvs:cigal:manual:chapter4:vecs|VECS(4)]]

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