error in Simulink matlab function

Hi

I encounter a problem. Matlab Function allows the matrix transposition:

y = fun(x) % x = [6,1]
x = x';
x
end

For my codes:

bPosGlobal = zeros(6,1)

function [y] =  OWScalcBodyWave(bPosGlobal)
y                     =  zeros(6,1);
rowNum                =  size(bPosGlobal,1)
columnNum             =  size(bPosGlobal,2)
if (rowNum            <  columnNum && rowNum >  1) || (rowNum >  columnNum && columnNum ==  1)
    bPosGlobal        =  bPosGlobal'; % Must be row vector
end
bPosGlobal
end

It reports:

Size mismatch between two arrays

Size mismatch (size [6][1] ~= size [1][6])

But when I comment out some codes, the error disappear:

function [y] =  OWScalcBodyWave(bPosGlobal)
y                     =  zeros(6,1);
rowNum                =  size(bPosGlobal,1)
columnNum             =  size(bPosGlobal,2)
% if (rowNum            <  columnNum && rowNum >  1) || (rowNum >  columnNum && columnNum ==  1)
bPosGlobal        =  bPosGlobal'; % Must be row vector
% end
bPosGlobal
end

Why this happens?

[Sam Chak]

Hi @tianyuan wang, by clicking the indentation icon , you can copy and paste the code in a format that resembles the MATLAB Editor environment.

[Chuguang Pan]

bPosGlobal = zeros(6,1);
OWScalcBodyWave(bPosGlobal);

rowNum = 6

columnNum = 1

bPosGlobal = 1×6

0 0 0 0 0 0

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function [y] =  OWScalcBodyWave(bPosGlobal)
    y                     =  zeros(6,1);
    rowNum                =  size(bPosGlobal,1)
    columnNum             =  size(bPosGlobal,2)
    if (rowNum            <  columnNum && rowNum >  1) || (rowNum >  columnNum && columnNum ==  1)
        bPosGlobal        =  bPosGlobal'; % Must be row vector
    end
    bPosGlobal
end

Answer 1

[Walter Roberson]

Simulink needs to be able to calculate the output size at compile time. Simulink is able to take into account formulas such as size(VARIABLE,DIMENSION) . However a condition such as

if (rowNum            <  columnNum && rowNum >  1) || (rowNum >  columnNum && columnNum ==  1)

is too complicated for it to be able to calculate the output size at compile time.

I think what you want to do is going to be difficult.

I think you should constrain the input to be appropriately sized and let that size propagate back.

Or consider using a Transopose block https://www.mathworks.com/help/simulink/slref/transpose.html possibly with an if/then/else block structure https://www.mathworks.com/help/simulink/slref/if.html