Diversion from paragraph 2B: plotting the .ump file

The MOPAC93 .ump file, obtained after a grid calculation, looks like this:
    1.900    1.900   58.541
    1.950    1.900   61.737
    2.000    1.900   64.764
    2.050    1.900   67.558
    2.100    1.900   70.135
    2.150    1.900   72.446
    2.200    1.900   74.478
    2.250    1.900   76.252
    2.300    1.900   77.730
    1.900    1.950   61.523
    1.950    1.950   64.560
    2.000    1.950   67.357
    2.050    1.950   69.893
    2.100    1.950   72.211
    2.150    1.950   74.116
    2.200    1.950   75.689
    2.250    1.950   76.874
    2.300    1.950   77.704
    1.900    2.000   64.234
    1.950    2.000   67.096
    2.000    2.000   69.673
    2.050    2.000   71.923
etc.
For Gnuplot to recognize these data as a grid, it is better to separate the rows (or columns) of the grid by blank lines:
    1.900    1.900   58.541
    1.950    1.900   61.737
    2.000    1.900   64.764
    2.050    1.900   67.558
    2.100    1.900   70.135
    2.150    1.900   72.446
    2.200    1.900   74.478
    2.250    1.900   76.252
    2.300    1.900   77.730

    1.900    1.950   61.523
    1.950    1.950   64.560
    2.000    1.950   67.357
    2.050    1.950   69.893
    2.100    1.950   72.211
    2.150    1.950   74.116
    2.200    1.950   75.689
    2.250    1.950   76.874
    2.300    1.950   77.704

    1.900    2.000   64.234
    1.950    2.000   67.096
    2.000    2.000   69.673
    2.050    2.000   71.923
etc.
Then use the following commands in Gnuplot:
set terminal X11
set contour base
set parametric
set cntrparam levels auto 20
set surface
set grid
set data style lines
splot 'filename.ump'
This results in the following plot:

In this example the variation along one diagonal is rather small. The 'cntrparam levels auto' number can be increased to 40 to make the saddle point more distinct.


Back to paragraph 2B.