The FIX statements is used in the METHODs part of a model to constrain particular variables in the model. A variable which has been fixed has a known value assigned to it, and ASCEND will not attempt to change that value. The FIXed variables in a model are used as the basis from which the remaining un-FIXed (FREE) variables can be calculated. By default, no variables are FIXed until an explicit command to FIX them is given.
(* add this to the example on the FIX page *) METHOD solve_x; (* reconfigure the model to solve for x such that y=0 *) FREE x; FIX y; y:= 0; END solve_x;
Note that variables can also be FIXed and FREEd in an ad-hoc way, using the ASCEND GUI.
See also FREE.