Break up cross-section into pieces

[GoogleCodeExporter]

The cross-section calc should be broken up into two parts like the dispersion 
calc is. The first should generate the analytic form and associated quantities 
and save them to a file. The second should read this file and compute the 
numerical results and plot them. This way, the often expensive task of 
computing the analytic form does not have to be repeated when a user simply 
wants to change the plot range or number of data points in the scan.

Original issue reported on code.google.com by wfly...@gmail.com on 16 Jul 2010 at 7:31

[GoogleCodeExporter]

The cross-section calc now calculates the cross-section expression and 
dispersion hamiltonian, then saves them to a temporary file. This file is then 
loaded and all numerical quantities are calculated and the results are plotted 
and saved. This allows the user to change omega and hkl ranges between plots 
without having to recalculate the cross-section analytically. 

Original comment by wfly...@gmail.com on 26 Jul 2010 at 8:42

• Changed state: Fixed