I created this restraint because I felt it might someday be needed, but I have yet to find a problem where it has been deployed. This option allows you to write your own equation that will be evaluated after substituting in values for GSAS-II parameters.
To create a general restraint, one selects the “General” tab and then uses the “Edit Restr.”/“Add restraint” menu command or the “Add restraint” button on the window. That opens a window where an expression can be entered as a single line of Python. That Python command can invoke math, numpy or GSAS-II routines or even your own external library of Python code. If that Python expression contains any variables, you will then assign GSAS-II parameters by name (see §24.1) to each of those variable. As an example, if the expression
10*x**2 + b*x + c
is entered, then you will be asked to supply GSAS-II parameters of form p:h:name for x, b and c. When evaluating \(\chi ^2\), the value for those parameters will be substituted into the expression and the result is placed as \(R_{calc,k}\). After creating the General restraint, the target value for the restraint, the \(\sigma \) value (labeled as esd) and the weight factor are entered in the data window.