Retrieve a single constraint matrix coefficient.
A non-zero return value indicates that a problem occurred while retrieving the coefficient. Refer to the Error Code table for a list of possible return values. Details on the error can be obtained by calling GRBgeterrormsg.
model: The model from which the coefficient should be retrieved.
constrind: The constraint index for the desired coefficient.
varind: The variable index for the desired coefficient.
valP: The location in which the requested matrix coefficient should be placed.
double A12; error = GRBgetcoeff(model, 1, 2, &A12);