Function SCIPinferVarFixProp 

pub unsafe extern "C" fn SCIPinferVarFixProp(
    scip: *mut SCIP,
    var: *mut SCIP_VAR,
    fixedval: f64,
    inferprop: *mut SCIP_PROP,
    inferinfo: c_int,
    force: c_uint,
    infeasible: *mut c_uint,
    tightened: *mut c_uint,
) -> SCIP_RETCODE

fixes variable in preprocessing or in the current node, if the new bound is tighter (w.r.t. bound strengthening epsilon) than the current bound; if possible, adjusts bound to integral value; the given inference constraint is stored, such that the conflict analysis is able to find out the reason for the deduction of the bound change

@note In presolving stage when not in probing mode the variable will be fixed directly, otherwise this method changes first the lowerbound by calling SCIPinferVarLbProp and second the upperbound by calling SCIPinferVarUbProp

@note If SCIP is in presolving stage, it can happen that the internal variable array (which get be accessed via SCIPgetVars()) gets re-sorted.

@note During presolving, an integer variable which bound changes to {0,1} is upgraded to a binary variable.