Note
Optimization Toolbox™ provides two approaches for solving single-objective optimization problems. This topic describes the problem-based approach. Solver-Based Optimization Problem Setup describes the solver-based approach.
To solve an optimization problem, perform the following steps.
Create an optimization problem object by using optimproblem
. A problem object is a container in which you
define an objective expression and constraints. The optimization problem object
defines the problem and any bounds that exist in the problem variables.
For example, create a maximization problem.
prob = optimproblem('ObjectiveSense','maximize');
Create named variables by using optimvar
. An optimization variable is a symbolic variable that
you use to describe the problem objective and constraints. Include any bounds in
the variable definitions.
For example, create a 15-by-3 array of binary variables named
'x'
.
x = optimvar('x',15,3,'Type','integer','LowerBound',0,'UpperBound',1);
Define the objective function in the problem object as an expression in the named variables.
Note
If you have a nonlinear function that is not composed of polynomials, rational
expressions, and elementary functions such as exp
, then convert the
function to an optimization expression by using fcn2optimexpr
.
See Convert Nonlinear Function to Optimization Expression and Supported Operations on Optimization Variables and Expressions.
If necessary, include extra parameters in your expression as workspace variables; see Pass Extra Parameters in Problem-Based Approach.
For example, assume that you have a real matrix f
of the
same size as a matrix of variables x
, and the objective is
the sum of the entries in f
times the corresponding variables
x
.
prob.Objective = sum(sum(f.*x));
Define constraints for optimization problems as either comparisons in the named variables or as comparisons of expressions.
Note
If you have a nonlinear function that is not composed of polynomials, rational
expressions, and elementary functions such as exp
, then convert the
function to an optimization expression by using fcn2optimexpr
.
See Convert Nonlinear Function to Optimization Expression and Supported Operations on Optimization Variables and Expressions.
For example, assume that the sum of the variables in each row of
x
must be one, and the sum of the variables in each
column must be no more than one.
onesum = sum(x,2) == 1; vertsum = sum(x,1) <= 1; prob.Constraints.onesum = onesum; prob.Constraints.vertsum = vertsum;
For nonlinear problems, set an initial point as a structure whose fields are the optimization variable names. For example:
x0.x = randn(size(x));
x0.y = eye(4); % Assumes y is a 4-by-4 variable
Solve the problem by using solve
.
sol = solve(prob);
% Or, for nonlinear problems,
sol = solve(prob,x0)
In addition to these basic steps, you can review the problem definition before solving
the problem by using show
or
write
. Set
options for solve
by using optimoptions
, as explained in Change Default Solver or Options.
Warning
The problem-based approach does not support complex values in an objective function, nonlinear equalities, or nonlinear inequalities. If a function calculation has a complex value, even as an intermediate value, the final result can be incorrect.
For a basic mixed-integer linear programming example, see Mixed-Integer Linear Programming Basics: Problem-Based or the video version Solve a Mixed-Integer Linear Programming Problem Using Optimization Modeling. For a nonlinear example, see Solve a Constrained Nonlinear Problem, Problem-Based. For more extensive examples, see Problem-Based Nonlinear Optimization, Linear Programming and Mixed-Integer Linear Programming, or Quadratic Programming and Cone Programming.
fcn2optimexpr
| optimoptions
| optimproblem
| optimvar
| show
| solve
| write