fitting functions with more independent variables

[James R. V. Z. <jr...@co...>]

Currently gnuplot has these data formats for fitting functions with
one or two independent variables:

      y
      x:y
      x:y:s
      x:y:z:s

I propose to implement these additional data formats for fitting
functions with 3-5 independent variables:

      v:x:y:z:s
      u:v:x:y:z:s
      t:u:v:x:y:z:s

For example, if there are five columns:

  The first column inherits its data range and time/date flag from the
  V axis unless a specific data range is given, and has the dummy
  variable 'v' unless a different name is given in a range or "set
  dummy v" statement.  The first range spec in a fit command would
  affect this variable.

  The second column inherits its data range and time/date flag from
  the first X axis unless a specific data range is given, and has the
  dummy variable 'x' unless a different name is given in a range or
  "set dummy x" statement.  The second range spec in a fit command
  would affect this variable.

  The third column inherits its data range and time/date flag from the
  first Y axis unless a specific data range is given, and has the
  dummy variable 'y' unless a different name is given in a range or
  "set dummy y" statement.

  The fourth column has the dependent variable, and inherits from the
  Z axis.

  The last column gives the error standard deviation.

Linear regression would look like this:

  h(v,x,y) = a*v + b*x + c*y
  fit h(v,x,y) 'foo.dat' using 1:2:3:4:(1) via a,b,c

  fit [q=-8:8] [r=*:*] [s=*:*] [t=0:10] a*q+b*r+c*s+d*t \
      'foo.dat' using 1:2:3:4:5:(1) via a,  b,  c,  d

I think I see how to do this.  

Comments?

         - Jim Van Zandt