if loop inside matlab function ----- i dont understand why this is not working

1 次查看（过去 30 天）

Ramu Nair R 2018-4-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/396623-if-loop-inside-matlab-function-i-dont-understand-why-this-is-not-working

编辑： Ramu Nair R 2018-9-8

function y = fcn(u)
  if(u>0.7) && (u<0.71)
    y=1;
  end

It gives error when put inside my simulink simulation:

Output argument 'y' is not assigned on some execution paths.
Function 'MATLAB Function' (#38.9.10), line 1, column 10:
"y"
Launch diagnostic report.
Component:MATLAB Function | Category:Coder error
Errors occurred during parsing of MATLAB function 'MATLAB Function'

11 个评论
显示 9更早的评论隐藏 9更早的评论

Stephan 2018-4-22

编辑：Walter Roberson 2018-9-8

在 MATLAB Online 中打开

function y = fcn(u) 
y=0;
if(u>0.7) && (u<0.71) && y=0
 y=1;
end

This could help to latch i guess

Ramu Nair R 2018-9-8

编辑：Ramu Nair R 2018-9-8

在 MATLAB Online 中打开

function y = fcn(u) 
y=0; 
if ((u>0.7) && (u<0.71) && y=0) 
y=1; 
end

I am getting the following error: Simulink cannot determine sizes and/or types of the outputs for block 'MATLAB Function' due to errors in the block body, or limitations of the underlying analysis. The errors might be inaccurate. Fix the indicated errors, or explicitly specify sizes and/or types for all block outputs.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Ameer Hamza 2018-4-22

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/396623-if-loop-inside-matlab-function-i-dont-understand-why-this-is-not-working#answer_316564

编辑：Ameer Hamza 2018-4-23

latching.mdl

Here is a event based solution to latch the value. The solution use if block and if action subsystem to latch the output once a certain condition is met. I used the clock as the input and the if condition becomes true between 20 to 21 seconds but output remains 1 after 20 seconds.

The Simulink model file is also attached.

13 个评论
显示 11更早的评论隐藏 11更早的评论

Walter Roberson 2018-9-8

在 MATLAB Online 中打开

Call that code with two parameters to force the output to be re-initialized to 0. The value of the second parameter does not matter, it just has to be two parameters.

However, this is not likely to be convenient to call with multiple parameters in Simulink.

For Simulink, you could use something like

function y = myfun(u)
  persistent value
  if isempty(value)
    value = 0;
  end
  if u>0.7 & u<0.71
    value = 1;
  end
  y = value;

This will only initialize the first time the block is run, and will not reinitialize unless some kind of clear is done such as if the model is unloaded.

You generally want more control over when the function will be reinitialized, so you would generally instead use a function block with two inputs, one of which controls reinitialization.

function y = myfun(u, init)
  persistent value
  if init
    value = 0;
  end
  if u>0.7 & u<0.71
    value = 1;
  end
  y = value;

This needs two inputs rather than one. The second input should be non-zero if you want to reinitialize, and should be 0 if you want to keep the current state. This differs from the use of init that dpb proposed in that dpb's proposal required that the function be called in different ways depending on what you wanted to do, which is a problem in Simulink.

Walter Roberson 2018-9-8

Making init optional is not feasible for Simulink use. You would need to disable a port by disconnecting it, or you would need to use enabled subsystems that turned off an input (and I do not know how Simulink is defined to behave in that case.)

Once placed and connected, any one Simulink block is expected to always be called with the same number of inputs.

Ramu Nair R 2018-9-8