Constraits allow you to automatically update parameters during your fit. Constraints can be simple, such as restricting a layer depth to a particular range, or complex, tying the value of one layer to another.
The change the constraints simply edit the code in the constraints window. This will make the Update button available. Pressing Update compiles the new constraints. If there is an error, a window will appear containing the text of the error on the top and the constraints program on the bottom. The line numbers in the error message should correspond to the line numbers in the constraints window. Pressing Show program displays the constraints program even if there were no errors.
Pressing Apply applies the constraints to the current layer profile. They are applied automatically during fits.
The constraints syntax is a variation on C syntax. In the current implementation constraints are converted to Tcl for processing. If for some reason you need more than the simple looping constructs and math functions available you can program Tcl constraints directly. In any case, no checks are done that the constraint code is correct, so be careful!
Constraints may be suspended with the gj2/mlayer command ULC. They are restored with the command LC, or by modifying the constraints and clicking Update.