particleswarm
Particle swarm optimization
Syntax
Description
attempts
to find a vector x
= particleswarm(fun
,nvars
)x
that achieves a local minimum
of fun
. nvars
is the dimension
(number of design variables) of fun
.
Note
Passing Extra Parameters explains how to pass extra parameters to the objective function, if necessary.
[
also returns the following, using any of the input
argument combinations in the previous syntaxes:x
,fval
,exitflag
,output
,points
]
= particleswarm(___)
fval
, a scalar that is the objective function valuefun(x)
exitflag
, a value that describes the exit conditionoutput
, a structure that contains information about the optimization processpoints
, a structure that contains the final swarm positions inpoints.X
and the associated objective function values inpoints.Fval
Examples
Minimize a Simple Function
Minimize a simple function of two variables.
Define the objective function.
fun = @(x)x(1)*exp(norm(x)^2);
Call particleswarm
to minimize the function.
rng default % For reproducibility nvars = 2; x = particleswarm(fun,nvars)
Optimization ended: relative change in the objective value over the last OPTIONS.MaxStallIterations iterations is less than OPTIONS.FunctionTolerance. x = 629.4474 311.4814
This solution is far from the true minimum, as you see in a function plot.
fsurf(@(x,y)x.*exp((x.^2+y.^2)))
Usually, it is best to set bounds. See Minimize a Simple Function with Bounds.
Minimize a Simple Function with Bounds
Minimize a simple function of two variables with bound constraints.
Define the objective function.
fun = @(x)x(1)*exp(norm(x)^2);
Set bounds on the variables.
lb = [10,15]; ub = [15,20];
Call particleswarm
to minimize the function.
rng default % For reproducibility nvars = 2; x = particleswarm(fun,nvars,lb,ub)
Optimization ended: relative change in the objective value over the last OPTIONS.MaxStallIterations iterations is less than OPTIONS.FunctionTolerance.
x = 1×2
0.7071 0.0000
Minimize Using Nondefault Options
Use a larger population and a hybrid function to try to get a better solution.
Specify the objective function and bounds.
fun = @(x)x(1)*exp(norm(x)^2); lb = [10,15]; ub = [15,20];
Specify the options.
options = optimoptions('particleswarm','SwarmSize',100,'HybridFcn',@fmincon);
Call particleswarm
to minimize the function.
rng default % For reproducibility nvars = 2; x = particleswarm(fun,nvars,lb,ub,options)
Optimization ended: relative change in the objective value over the last OPTIONS.MaxStallIterations iterations is less than OPTIONS.FunctionTolerance.
x = 1×2
0.7071 0.0000
Examine the Solution Process
Return the optional output arguments to examine the solution process in more detail.
Define the problem.
fun = @(x)x(1)*exp(norm(x)^2); lb = [10,15]; ub = [15,20]; options = optimoptions('particleswarm','SwarmSize',50,'HybridFcn',@fmincon);
Call particleswarm
with all outputs to minimize the function and get information about the solution process.
rng default % For reproducibility nvars = 2; [x,fval,exitflag,output,points] = particleswarm(fun,nvars,lb,ub,options)
Optimization ended: relative change in the objective value over the last OPTIONS.MaxStallIterations iterations is less than OPTIONS.FunctionTolerance.
x = 1×2
0.7071 0.0000
fval = 0.4289
exitflag = 1
output = struct with fields:
rngstate: [1x1 struct]
iterations: 43
funccount: 2203
message: 'Optimization ended: relative change in the objective value ...'
hybridflag: 1
points = struct with fields:
X: [50x2 double]
Fval: [50x1 double]
Input Arguments
fun
— Objective function
function handle  function name
Objective function, specified as a function handle or function name. Write the objective
function to accept a row vector of length
nvars
and return a scalar
value.
When the 'UseVectorized'
option is true
, write
fun
to accept a
pop
bynvars
matrix, where pop
is the current
population size. In this case,
fun
returns a vector the same
length as pop
containing the
fitness function values. Ensure that
fun
does not assume any
particular size for pop
, since
particleswarm
can pass a single
member of a population even in a vectorized
calculation.
Example: fun = @(x)(x[4,2]).^2
Data Types: char
 function_handle
 string
nvars
— Number of variables
positive integer
Number of variables, specified as a positive integer. The solver passes row vectors of length
nvars
to fun
.
Example: 4
Data Types: double
lb
— Lower bounds
[]
(default)  real vector or array
Lower bounds, specified as a real vector or array of doubles. lb
represents
the lower bounds elementwise in
lb
≤ x
≤ ub
.
Internally, particleswarm
converts an array lb
to the
vector lb(:)
.
Example: lb = [0;Inf;4]
means x(1) ≥ 0
, x(3) ≥ 4
.
Data Types: double
ub
— Upper bounds
[]
(default)  real vector or array
Upper bounds, specified as a real vector or array of doubles. ub
represents
the upper bounds elementwise in
lb
≤ x
≤ ub
.
Internally, particleswarm
converts an array ub
to the
vector ub(:)
.
Example: ub = [Inf;4;10]
means x(2) ≤ 4
, x(3) ≤ 10
.
Data Types: double
options
— Options for particleswarm
options created using optimoptions
Options for particleswarm
, specified as the
output of the optimoptions
function.
Some options are absent from the optimoptions
display.
These options are listed in italics. For details, see View Optimization Options.
CreationFcn  Function that creates the initial swarm. Specify as

Display  Level of display returned to the command line.

DisplayInterval  Interval for iterative display. The iterative display prints
one line for every DisplayInterval iterations.
Default is 1 . 
FunctionTolerance  Nonnegative scalar with default 1e6 . Iterations
end when the relative change in best objective function value over
the last MaxStallIterations iterations is less
than options.FunctionTolerance . 
FunValCheck  Check whether objective function
and constraints values are valid. 
HybridFcn  Function that continues the optimization after
Can also be a cell array specifying the
hybrid function and its options, such as

InertiaRange  Twoelement real vector with same sign values in increasing
order. Gives the lower and upper bound of the adaptive inertia. To
obtain a constant (nonadaptive) inertia, set both elements of InertiaRange to
the same value. Default is [0.1,1.1] . See Particle Swarm Optimization Algorithm. 
InitialPoints  Initial population or partial population of particles, specified as a matrix or a structure.

InitialSwarmSpan  Initial range of particle positions that

MaxIterations  Maximum number of iterations particleswarm takes.
Default is 200*nvars , where nvars is
the number of variables. 
MaxStallIterations  Positive integer with default 20 . Iterations
end when the relative change in best objective function value over
the last MaxStallIterations iterations is less
than options.FunctionTolerance . 
MaxStallTime  Maximum number of seconds without an improvement in the best
known objective function value. Positive scalar with default Inf . 
MaxTime  Maximum time in seconds that particleswarm runs.
Default is Inf . 
MinNeighborsFraction  Minimum adaptive neighborhood size, a scalar from 0 to 1 .
Default is 0.25 . See Particle Swarm Optimization Algorithm. 
ObjectiveLimit  Minimum objective value, a stopping criterion. Scalar, with
default Inf . 
OutputFcn  Function handle or cell array of function handles. Output functions can read iterative data,
and stop the solver. Default is [] . See
Output Function and Plot Function. 
PlotFcn  Function name, function handle, or cell array of function handles. For custom plot functions,
pass function handles. Plot functions can read iterative
data, plot each iteration, and stop the solver. Default is
[] . Available builtin plot function:
'pswplotbestf' . See Output Function and Plot Function. 
SelfAdjustmentWeight  Weighting of each particle’s best position when adjusting
velocity. Finite scalar with default 1.49 . See Particle Swarm Optimization Algorithm. 
SocialAdjustmentWeight  Weighting of the neighborhood’s best position when adjusting
velocity. Finite scalar with default 1.49 . See Particle Swarm Optimization Algorithm. 
SwarmSize  Number of particles in the swarm, an integer greater than 1 .
Default is min(100,10*nvars) , where nvars is
the number of variables. 
UseParallel  Compute objective function in parallel when true .
Default is false . See Parallel or Vectorized Function Evaluation. 
UseVectorized  Compute objective function in vectorized fashion when true .
Default is false . See Parallel or Vectorized Function Evaluation. 
problem
— Optimization problem
structure
Optimization problem, specified as a structure with the following fields.
solver  'particleswarm' 
objective  Function handle to the objective function, or name of the objective function. 
nvars  Number of variables in problem. 
lb  Vector or array of lower bounds. 
ub  Vector or array of upper bounds. 
options  Options created by optimoptions . 
rngstate  Optional state of the random number generator at the beginning of the solution process. 
Data Types: struct
Output Arguments
x
— Solution
real vector
Solution, returned as a real vector that minimizes the objective function subject to any bound constraints.
fval
— Objective value
real scalar
Objective value, returned as the real scalar fun(x)
.
exitflag
— Algorithm stopping condition
integer
Algorithm stopping condition, returned as an integer identifying
the reason the algorithm stopped. The following lists the values of exitflag
and
the corresponding reasons particleswarm
stopped.
 Relative change in the objective value over the last 
 Number of iterations exceeded 
 Iterations stopped by output function or plot function. 
 Bounds are inconsistent: for some 
 Best objective function value is below

 Best objective function value did not change within 
 Run time exceeded 
output
— Solution process summary
structure
Solution process summary, returned as a structure containing information about the optimization process.
 Number of solver iterations 
 Number of objective function evaluations. 
 Reason the algorithm stopped. 
 Exit flag from the hybrid function. Relates to the

 State of the default random number generator just before the algorithm started. 
points
— Final swarm positions and objective function values
structure
Final swarm positions and objective function values, returned as a structure with these fields:
X
— Positions of the final swarm, returned as a matrix. Each row of the matrix represents one point.Fval
— Objective function values of the final swarm. For eachi
, an index of a member of the final swarm,points.Fval(i) = fun(points.X(i))
.
To continue an optimization, you can pass points
as the
InitialPoints
option. However, this approach is not
the same as running an optimization for a longer time from the beginning,
because many aspects of the algorithm are not identical when the
optimization restarts from a final population. See Particle Swarm Optimization Algorithm.
Data Types: struct
Limitations
The problembased Optimize Live Editor task currently does not support specifying multiple initial points or initial objective function values. To specify initial points, use the solverbased task, or use the command line.
Algorithms
For a description of the particle swarm optimization algorithm, see Particle Swarm Optimization Algorithm.
Alternative Functionality
App
The Optimize Live Editor task provides a visual interface for particleswarm
.
Extended Capabilities
Automatic Parallel Support
Accelerate code by automatically running computation in parallel using Parallel Computing Toolbox™.
To run in parallel, set the 'UseParallel'
option to true
.
options = optimoptions('
solvername
','UseParallel',true)
For more information, see How to Use Parallel Processing in Global Optimization Toolbox.
Version History
Introduced in R2014bR2023b: Specify and obtain particleswarm
initial points, final positions, and objective function values
particleswarm
can now return the output
points
, a structure containing the final positions and
associated objective function values of the swarm. You can now provide the positions
and objective function values for the initial swarm using the
InitialPoints
option. You can still provide the initial swarm
positions using the InitialSwarmMatrix
option or the
InitialSwarm
option. In these cases,
particleswarm
passes the initial swarm matrix as the
InitialPoints
option.
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