Set a single value in a string-valued array attribute.
A non-zero return value indicates that a problem occurred while setting the attribute. Refer to the Error Code table for a list of possible return values. Details on the error can be obtained by calling GRBgeterrormsg.
model: A loaded optimization model, typically created by routine GRBnewmodel or GRBreadmodel.
attrname: The name of a string-valued array attribute. Available attributes are listed and described in the Attributes section of this document.
element: The index of the array element to be changed.
newvalue: The value to which the attribute element should be set.
Note that this method should be used for array attributes only (i.e., variable or constraint attributes). To modify a scalar attribute (i.e., a model attribute), use GRBsetstrattr instead.
error = GRBsetstrattrelement(model, "ConstrName", 0, "NewConstr");