Simulink considers that an output matrix has variable size when the size is always constant

Hi! I'm running a code in simulink (in one of the matlab function blocks) and I keep getting errors regarding the size of the output matrix. My code is the following one, where phi_1 is a ramp input that goes from 0 to 2*pi, and all the values in perm are constants:

function Ga = G(phi_1,perm)
G_amax=perm(1);
n=perm(2);
ns=perm(5);
nr=perm(6);
gamma=perm(3);
gammap=perm(4);
Ga=zeros(nr,ns);
%define angles between rotor (rows) and stator (columns) teeth
phi=zeros(nr,ns);
phi(1,1)=phi_1;
phi(2,1)=phi(1,1) + 2*pi/nr;

for j=2:ns
    phi(1,j)=phi(1,j-1) - 2*pi/ns;
    phi(2,j)=phi(1,j) + 2*pi/nr;
end
%make sure that the angle is in the first fifth (it's periodic every 1/5th
%of a turn)
for j=1:nr
    for k=1:ns
        while phi(j,k)<0
            phi(j,k)=phi(j,k)+2*pi;
        end
        while phi(j,k)>2*pi/5
            phi(j,k)=phi(j,k)-2*pi/5;
        end
        %permeances as a function of the angle
        if 0<=phi(k,j) && phi(k,j)<gammap || 2*pi/n - gammap<=phi(k,j) && phi(k,j)<=2*pi/n
            Ga(k,j)=G_amax;
        elseif gammap<=phi(k,j) && phi(k,j)<=gamma
            Ga(k,j)=G_amax/2 * (1+cos(pi*(phi(k,j)-gammap)/(gamma-gammap)));
        elseif 2*pi/n - gamma<=phi(k,j) && phi(k,j)<=2*pi/n - gammap
            Ga(k,j)=G_amax/2 * (1+cos(pi*(phi(k,j)-2*pi/n+gammap)/(gamma-gammap)));
        else
            Ga(k,j)=0;
        end
    end
end

When I run the simulation, I get the following error:

Error:A signal of unbounded array type is not supported on 'Input Port 1' of block 'air_gap/Scope2'. For a list of supported data types, see the block documentation page.

If I try setting the size of the matrix Ga to the one that it's supposed to have ([2,3]) in the explore section instead of the predetermined -1, I get this error:

Error:The signal at 'Output Port 1' of 'air_gap/MATLAB Function2' is a variable-size signal with a nondiscrete sample time. The sample time for any variable-size signal must be discrete.

However, I want to be able to use continuous signals instead of discrete ones. Is there a way to do so? And if not, how do I switch it to discrete?

Thanks!

[Fangjun Jiang]

What is "perm"? An input to the MATLAB Function block?

[Inés Deiros Gras]

Perm is just a matrix I defined in MATLAB and inputed as a constant block. It is defined as follows:

Gamax=10;

n=5;

nr=2;

ns=3;

gamma=3*pi/15;

gammap=gamma/2;

perm=[Gamax,n,gamma,gammap,ns,nr];

Answer 1

[Fangjun Jiang]

You have "Ga=zeros(nr,ns)" so the size of Ga is fixed in your mind. But it is not the case for Simulink. Since nr and ns all come from input. Their value could change during simulation thus the size of Ga could be varying.

In the MATLAB Function block, change the scope of "perm" from "Input" to "Parameter". It will still appear in the function code input argument, but it will not appear as an input port in the MATLAB Function block. Define "perm" in the base workspace.

Hopefully, that will fixed the "variable size" error.

[Inés Deiros Gras]

Thank you very much, I think this solved the problem with the Ga matrix, but now I get the following error:

Error:A signal of unbounded array type is not supported on 'Input Port 1' of block 'air_gap/Scope2'. For a list of supported data types, see the block documentation page.

Do you know what this might mean and how I can solve it?

Thanks again for your help!!

[Fangjun Jiang]

The error message is the same. It didn't resolve the problem.

You need to do one more thing. Double click "perm" to open its properties. un-check "Tunable" option. The variable size issue will be resolved.

You will have other error. It seems it should be phi(j,k), Ga(j,k) in many places, not phi(k,j), Ga(k,j)

[Inés Deiros Gras]

You were right, I got the phi(k,j) and Ga(k,j) messed up in some places, thank you! However, when I run the code again, after un-checking the "Turnable" option I still get the same error. Do you know what else I could do? The corrected function is the following one, in case it helps:

function Ga = G(phi_1,perm)

G_amax=perm(1);

n=perm(2);

ns=perm(5);

nr=perm(6);

gamma=perm(3);

gammap=perm(4);

Ga=zeros(nr,ns);

%define angles between rotor (rows) and stator (columns) teeth

phi=zeros(nr,ns);

phi(1,1)=phi_1;

phi(2,1)=phi(1,1) + 2*pi/nr;

for j=2:ns

phi(1,j)=phi(1,j-1) - 2*pi/ns;

phi(2,j)=phi(1,j) + 2*pi/nr;

end

%make sure that the angle is in the first fifth (it's periodic every 1/5th

%of a turn)

for j=1:nr

for k=1:ns

while phi(j,k)<0

phi(j,k)=phi(j,k)+2*pi;

end

while phi(j,k)>2*pi/5

phi(j,k)=phi(j,k)-2*pi/5;

end

%permeances as a function of the angle

if 0<=phi(j,k) && phi(j,k)<gammap || 2*pi/n - gammap<=phi(j,k) && phi(j,k)<=2*pi/n

Ga(j,k)=G_amax;

elseif gammap<=phi(j,k) && phi(j,k)<=gamma

Ga(j,k)=G_amax/2 * (1+cos(pi*(phi(j,k)-gammap)/(gamma-gammap)));

elseif 2*pi/n - gamma<=phi(j,k) && phi(j,k)<=2*pi/n - gammap

Ga(j,k)=G_amax/2 * (1+cos(pi*(phi(j,k)-2*pi/n+gammap)/(gamma-gammap)));

else

Ga(j,k)=0;

end

end

end

[Fangjun Jiang]

no error at all.

[Inés Deiros Gras]

Thank you very much!! I don't know what I was doing before, but I started a new file and now it works. Thanks a lot!!!