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

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Inés Deiros Gras 2024-5-12

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评论： Inés Deiros Gras 2024-5-20

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!

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Fangjun Jiang 2024-5-13

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

Inés Deiros Gras 2024-5-13

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];

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Answer 1

Fangjun Jiang 2024-5-14

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2117856-simulink-considers-that-an-output-matrix-has-variable-size-when-the-size-is-always-constant#answer_1457301

编辑：Fangjun Jiang 2024-5-14

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.

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Inés Deiros Gras 2024-5-16

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

Fangjun Jiang 2024-5-16

no error at all.

Inés Deiros Gras 2024-5-20

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!!!

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