If else condition is not working properly in matlab function block

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Nandhini 2023-9-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026839-if-else-condition-is-not-working-properly-in-matlab-function-block

评论： Nandhini 2023-9-29

function [y1,y2]= fcn(u1,u2,u3,u4)
if u1 > 5
    y1=u2;
else y1=u3;
end
if u1 < 5
    y2=u3;
else y2=u2;
end

I implemented this function in MATLAB function but my output of MATLAB function block always comes as 5 it is not taking the input properely and it is also showing 5 when it is really less than 5 also,here iam giving this output to controlled current source.

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dpb 2023-9-28

编辑：dpb 2023-9-28

在 MATLAB Online 中打开

function [y1]= fcn(u1,u2,u3)
  if u1 > 5
    y1=u2;
  else
    y1=u3;
  end
end

Be better/more consistent with formatting and will be easier to read/debug code as @Adam suggested earlier. Also, use the "CODE" formatting button to format your code here...

The above function has nothing wrong with it, per se, whatever issues you have are somehow tied to the model -- I note the output of the function block is highlighted in yellow and says "Inaccessible" -- that implies to me something, somehow isn't right, but I don't have and have never used Simulink so can't comment/help on the actual process of using a MATLAB function in/with it, but there would seem to be where your problems lie...clearly if the function is being called with the desired inputs, it will as far as it alone is concerned return either one or the other of the two inputs based on the first.

If it isn't, then either it isn't getting called or the inputs aren't what you think they are or the fact there seems to be a warning/error message on the model about that output signal means it is just using some substitute value instead (effectively the first case above of not being called).

Methinks you need to create a very simple model that calls a function and get it to work standalone to understand that use first...

Sam Chak 2023-9-29

Hi @Nandhini

I have attached the plots of the u1 and y1 signals (Scope 2 and Scope 3, respectively). The code in the MATLAB Function block works as expected. What is the desired signal for y1? It may be possible to construct the function mathematically.

Blocks under the Masked system (Speed regulator PI controller):

u1 signal:

y1 signal:

Nandhini 2023-9-29

Hi thank you for the comment.I have another doubt,i want to check this loop after the half of simulation time,so that i can avoid intial oscillations.for example i want to avoid the first 0.5s simulation time for this MATLAB function loop,kindly help me how this can be implemented.

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回答（1 个）

Amir Azadeh Ranjbar 2023-9-28

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026839-if-else-condition-is-not-working-properly-in-matlab-function-block#answer_1321114

在 MATLAB Online 中打开

If you want me to provide better guidance, please tell me more about your goal for writing this function.

function [y1,y2]= fcn(u1,u2,u3,u4)
if u1>=5
    y1 = u2 ;
else
    y2 = u3 ;
end
end

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dpb 2023-9-28

编辑：dpb 2023-9-28

在 MATLAB Online 中打开

That's not the function he simplified to and says still not functional...and

function [y1,y2]= fcn(u1,u2,u3,u4)
if u1>=5
    y1 = u2 ;
else
    y2 = u3 ;
end
end

is NOT what the original actually reduces to; while inefficiently written with the two independent blocks it is the same as

function [y1,y2]= fcn(u1,u2,u3)
  if u1>5
    y1 = u2;
    y2 = u2;
  else
    y1 = u3;
    y2 = u3;
  end
end

also removing the superfluous input argument.

ADDENDUM: As @Walter Roberson questions, as written the original will do the "else" clause for u1==5; that may not have been the intended action in which case if the case of 5 were tested, there wouldn't be any change from the u1<5 case, but it should have behaved differently than u1==10.

As for intent, that seems pretty clear from his earlier statement -- I would have to try to dig into the actual model much more to see if the logic in its construction is such as to accomplish that, but the intent seems clear enough:

"I am trying to control the controlled current source based on the ouput of MATLAB function,but whenever i kept the thershold as 5 or 10 it is showing same as the output." --@Nandhini

The problem isn't in the function per se (as revised) but in its use in the model -- and there I've no hands-on experience at all, but the "inaccessible" message on the output of the function block signal trace would seem to be a very big klew something ain't right...