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

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.

Answer 1

[AJ von Alt]

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

Replacing

x=value(ind);

with

x=value(ind(1));

should fix this.

[ameen]

Thank you very much for your kind reply which fix my problem however, the generated numbers are not varying according to my for loop. Numbers generated every 2 seconds if the time of simulation is 100 and generated every 20 seconds if the time of simulation is 1000 !!!!!!!!

My for loop doesn't make any difference. What should be done to fix this problem ???

What i am trying to do is generating random number every 10 of the simulation time which can be different in many simulations. so, i used a clock block in simulink and make the code function of time as follows:

function x = fcn(time)

x=0;

for time=0:10:time; 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(1));

end

Many Thanks in advance

[AJ von Alt]

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;

[ameen]

Thank you very much for your help, i really appreciate it.