Create with understanding

From ASCEND

A key feature of ASCEND is the ability to FIX and FREE models via the user interface, on-the-fly, without editing the text-file description of your model. This is a bit similar to repeatedly running the 'Solver' feature of Excel, for example, but with different 'target' values and different 'variables' each time.

ASCEND will re-analyse the system of equations each time you change the fixed and free variables in your model, and will (with the standard QRSlv solver) form a block-decomposed format so that equations can be solved efficiently and in a logical sequence. You can inspect the incidence matrix of your system to see what the implications are of chosing to fix/free various combinations of variables.