output variable size matrix, while its specified type is something else.

Question

ameen 2014-9-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/154282-output-variable-size-matrix-while-its-specified-type-is-something-else

评论： ameen 2014-9-11

采纳的回答： AJ von Alt

Hi There

I want to generate random number based on its probability and i found the following code online

for time1=0:10:100;

r=rand;

prob=[.5,.1,.4];

prob=cumsum(prob);

value=[6,7,8]; %values corresponding to the probabilities

ind=find(r<=prob,1,'first');

x=value(ind)

end

it is working fine on Matlab however on Simulink it gives me the following error:

''Data 'x' (#79) is inferred as a variable size matrix, while its specified type is something else. ''

I changed the size of x and makes it 'variable size' then i received the following message:

''Output 'x' (#79) has variable size but the upper bound is not specified; explicit upper bound must be provided. ''

What i Want is: generating one random number from (6, 7, 8) based on its probability at each for loop.

Many Thanks in advance.

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Answer 1

AJ von Alt 2014-9-10

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https://ww2.mathworks.cn/matlabcentral/answers/154282-output-variable-size-matrix-while-its-specified-type-is-something-else#answer_151295

在 MATLAB Online 中打开

MATLAB Function Block is having difficulty inferring the size of x.

Replacing

x=value(ind);

with

x=value(ind(1));

should fix this.

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AJ von Alt 2014-9-11

在 MATLAB Online 中打开

It's not clear what the intended behavior is.

The entirety of the code in the MATLAB Function block is executed at each time step. Since x is overwritten at each iteration, only the last value calculated is ever output.

If you want to output the same value for 10 seconds and then draw a new random value, you could change the sample time of the block to match that or use persistent variables to store the last drawn random value and the time that it was drawn and then update them only when the change in time has surpassed a threshold.

function out = fcn( time )
persistent tLast
persistent rValLast
if isempty( tLast ) || ( time - tLast ) > 10 
    tLast = time;
    rValLast = % update random value here
end
out = rValLast;