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lines 5-66 of file: src/fix_constraint.xrst
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{xrst_begin fix_constraint}

User Defined Fixed Effects Constraint Function
##############################################

Syntax
******
*vec* = *mixed_object* . ``fix_constraint`` ( *fixed_vec* )

mixed_object
************
We use :ref:`derived_ctor@mixed_object`
to denote an object of a class that is
derived from the ``cppad_mixed`` base class.

a1_double
*********
see :ref:`typedef@Scalar Types@a1_double` .

Virtual Function
****************
The following virtual function may be implemented in the derived class:

| |tab| ``virtual CppAD::vector<a1_double> fix_constraint`` (
| |tab| |tab| ``const CppAD::vector<a1_double>&`` *fixed_vec*
| |tab| )

fixed_vec
*********
This argument has prototype

    ``const CppAD::vector<a1_double>&`` *fixed_vec*

It contains a value for the
:ref:`fixed effects<problem@Notation@Fixed Effects, theta>` vector.

vec
***
This result has prototype

    ``CppAD::vector<`` *a1_double* > *vec*

It is the value of the
:ref:`constraint function<problem@Maximum Likelihood@Fixed Constraints, c>`
:math:`c( \theta)`

Default
=======
The base class definition (default) for ``fix_constraint``
returns an empty vector;
i.e., *vec* . ``size`` () == 0 .
In the case where there are no constraints of this form.
{xrst_toc_hidden
    example/user/fix_constraint.cpp
}
Example
*******
The file :ref:`fix_constraint.cpp-name` contains an example
using constraints.
It returns true, if the test passes, and false otherwise.

{xrst_end fix_constraint}