relationship between contrasts in the custom model vs the gui

[LukeAClifton]

Often in NR fitting we often fit an experimental process.

A common example would be a bare substrate, then substrate plus lipid bilayer, then substrate plus bilayer plus protein.

In rascal 1 you can define cases in the custom models to enable you to fit an experimental process in a single project:

switch contrast
case {1}
output = [SILICONOXIDE];
case {2}
output = [SILICONOXIDE; HEADGROUPS; TAILS; HEADGROUPS];
case {3}
output = [SILICONOXIDE; HEADGROUPS; TAILS; HEADGROUPS];

end

These cases are directly linked to the contrast tabs in the gui - which is intuitive.

In rascal 2 you can also defne cases in the custom model (python example below):

match contrast:
    case 0 | 1:
       output = np.array([oxide]) 
    case 2:
        output = np.array([oxide, Head_D2O, Tail, Tail, Head_D2O])
    case 3:
        output = np.array([oxide, Head_SMW, Tail, Tail, Head_SMW])
    case 4:
        output = np.array([oxide, Head_H2O, Tail, Tail, Head_H2O])

However, its not not clear how these contrast relate to the contrast list in the GUI which are only define by name. Having this link more clearly defined would be useful.