How to fix : Unable to perform assignment because the left and right sides have a different number of elements.

I am trying to use particle swarm optimization to solve a problem of mine.

And i get following error:

Unable to perform assignment because the left and right sides have a

different number of elements.

This is the initial code:

function output= fun(X)
g(:,1)=[2;2]; R1=X(:,1); R3=X(:,2); R2= R3-g;  n=X(:,3);

Br1=1.2;Br2=1.2;mu=4.*pi.*10.^-7;R4=35; 
Length=70; L=2.*pi.*sqrt((R4.^2+R1.^2)./2);
x=(Br1.*Br2.*L.*(10^-6))/(4.*pi.*mu);
a=Length./n; 
b=R2-R1;
d=R4-R3;
h=R3-R2;
c=-10:0.5:0;
F=0; 

I feel there is an issue with how i have defined the variables.

[Dyuman Joshi]

What is the full error and in which line does it occur?

Mention the code that is relevant to the line where the error occurs.

[Supreeth D K]

This is the PSO code i have used and error occurs in line 152

clc;

clear;

close all;

%% Problem Definition

run=5;

for i=1:run

CostFunction = @(X)-fun(X); % maximizing Function

nVar = 3; % Number of parameter

VarSize = [1 nVar]; % Size of Decision Variables Matrix

VarMin = [10 0.5 1]; % Lower Bound of parameters

VarMax = [40 5.5 2.5]; % Upper Bound of parameters

%% PSO Parameters

MaxIt = 1000; % Maximum Number of Iterations

nPop = 50; % Population Size (Swarm Size)

% PSO Parameters

w = 1; % Inertia Weight

wdamp = 0.99; % Inertia Weight Damping Ratio

c1 = 1; % Personal Learning Coefficient

c2 = 1.5; % Global Learning Coefficient

% Velocity Limits

VelMax = 0.1*(VarMax-VarMin);

VelMin = -VelMax;

%% Initialization

empty_particle.Position = [];

empty_particle.Cost = [];

empty_particle.Velocity = [];

empty_particle.Best.Position = [];

empty_particle.Best.Cost = [];

particle = repmat(empty_particle, nPop, 1);

GlobalBest.Cost = inf;

for i = 1:nPop

% Initialize Position

particle(i).Position = unifrnd(VarMin, VarMax, VarSize);

% Initialize Velocity

particle(i).Velocity = zeros(VarSize);

% Evaluation

particle(i).Cost = CostFunction(particle(i).Position);

% Update Personal Best

particle(i).Best.Position = particle(i).Position;

particle(i).Best.Cost = particle(i).Cost;

% Update Global Best

if particle(i).Best.Cost<GlobalBest.Cost

GlobalBest = particle(i).Best;

end

end

BestCost = zeros(MaxIt, 1);

%% PSO Main Loop

for it = 1:MaxIt

for i = 1:nPop

% Update Velocity

particle(i).Velocity = w*particle(i).Velocity ...

+c1*rand(VarSize).*(particle(i).Best.Position-particle(i).Position) ...

+c2*rand(VarSize).*(GlobalBest.Position-particle(i).Position);

% Apply Velocity Limits

particle(i).Velocity = max(particle(i).Velocity, VelMin);

particle(i).Velocity = min(particle(i).Velocity, VelMax);

% Update Position

particle(i).Position = particle(i).Position + particle(i).Velocity;

% Velocity Mirror Effect

IsOutside = (particle(i).Position<VarMin | particle(i).Position>VarMax);

particle(i).Velocity(IsOutside) = -particle(i).Velocity(IsOutside);

% Apply Position Limits

particle(i).Position = max(particle(i).Position, VarMin);

particle(i).Position = min(particle(i).Position, VarMax);

% Evaluation

particle(i).Cost = CostFunction(particle(i).Position);

% Update Personal Best

if particle(i).Cost<particle(i).Best.Cost

particle(i).Best.Position = particle(i).Position;

particle(i).Best.Cost = particle(i).Cost;

% Update Global Best

if particle(i).Best.Cost<GlobalBest.Cost

GlobalBest = particle(i).Best;

end

end

end

BestCost(it) = GlobalBest.Cost;

w = w*wdamp;

end

BestSol = GlobalBest;

disp(BestSol);

end

%% Results

figure;

%plot(BestCost, 'LineWidth', 2);

semilogy(BestCost, 'LineWidth', 2);

xlabel('Iteration');

ylabel('Best Cost');

grid on;

Answer 1

[KSSV]

This is a simple error, it occurs when you try to save more number of elements into an array than it is initialized for.

Ex:

A = zeros(1,3) ; 
A(1) = rand ; % filling one element in one position 
A(2) = rand(1,2) ; % filling two elements in one position; not correct so error

Unable to perform assignment because the left and right sides have a different number of elements.