Error in Genetic Algorithm: Input arguments to function include colon operator. To input the colon character, use ':' instead.

I'm trying to run GA for a structural problem and I'm ending up with the error:

"Input arguments to function include colon operator. To input the colon character, use ':' instead."

I'm not able to find where the problem is. This is my code:

function C = fitnessmin(x)
%%constatns
q = 33e4;
H = 5;
g = 9.8;
L = 30;
DI = 2700;
DS = 2700;
ES = 70e9;
FSIbeam = 270e6;
FSSupport = 170e6;
cIbeam = 2.05;
cSupport = 2.05;
%%Mass
%%Ibeams
MIbeam = (2*x(1)*x(3) + (x(2) - 2*x(3))*x(3))*L*DI*x(6);
%%Support
MSupport = x(4)*x(5)*H*DS;
%%function
C = cIbeam*MIbeam + cSupport*MSupport;
end

function [c, ceq] = constraintmin(x)
%%constatns
L = 30;
q = 33e4;
H = 5;
g = 9.8;
DI = 2700;
DS = 2700;
ES = 70e9;
FSIbeam = 270e6;
FSSupport = 170e6;
%%Mass
%%Ibeams
MIbeam = (2*x(1)*x(3) + (x(2) - 2*x(3))*x(3))*L*DI*x(6);
%%Support
MSupport = x(4)*x(5)*H*DS;
%%Equations
MOIIbeam = (((x(2) - 2*x(3))^3)*x(3)/12) + 2*(((x(3)^3)/12) + x(3)*x(1)*((x(2)/2) - (x(3)/2))^2);

SIbeam = (q*((L/2)^2) + MIbeam*(L/4)*g)*(x(2)/2)/(8*MOIIbeam*x(6));

SSIbeam = (MIbeam*g + q*L)/(4*x(6)*(2*x(1)*x(3)) + (x(2) - 2*x(3))*x(3));

Pcrit = (pi*pi)*ES*min(((x(4)^3)*x(5)/12), (x(4)*(x(5)^3)/12));

Papplied = MIbeam*g + q*L/(2);

SSupport = Papplied/(x(4)*x(5))
%%Function

c = [SIbeam - FSIbeam; SSIbeam - FSIbeam; Papplied - Pcrit; SSupport - FSSupport];
ceq = [];

end

clear
clc
objectivefunction = @fitnessmin;
nvars = 6;
lb = [0 0 0 0 0 1];
ub = [1 1 1 1 1 4];
constraintfunction = @constraintmin;
[x,fval] = ga(objectivefunction, nvars, [], [], [], [], lb, ub, [], constraintfunction)

Any help is appreciated. Thanks!

Answer 1

[Walter Roberson]

The [] before constraintfun should not be there in the ga call. After lower bound is nonlinear constraint, and after that would be integer constraint (optional) and then options (optional) -- if both appear it must be in that order.

If you fix that then you will still have problems. In your constraint you define SSupport = Papplied / (x(4)*x(5)) . If either x(4) or x(5) are zero, then that is a division by 0 which leads to infinity which is not a permitted output from a constraint function. Your lower bounds are both 0 for x(4) and x(5) so it is possible for either or both of them to be 0.

[Praneeth Arcot]

Yes thank you! I just found out that seconds ago. And I did change the bounds to make sure the values doesn't go inf. Cheers!