=polyfit function give error in matlab app designer app

p = polyfit(x, y, 1); with arrays shown below.

When executed in the app, error is given :

"Error using polyfit (line 44)

X and Y vectors must be the same size."

When the same poly fit function is executed from the command window in matlab ( and putting the variables in workspace). the function works as expected.

For extra insight, the x and y variables are concatinated before using the poly function with the following code:

where xneg is columns 1 - 7(backwards) and yneg is 1-7 ( was originaly part of a larger array)

x = [flip(xneg); xpos];

y = [yneg(1:7) ypos];

Any help or insight would be greatly appriciated!

Answer 1

[Binaya]

Hi Collin

The error indicates that the values or sizes of "x" and "y" differ when used in App Designer. This issue arises because apps created with MATLAB App Designer do not use the base MATLAB workspace, which is why the same command may not throw an error in the command window.

To check the values of "x" and "y" in the App's workspace, add a breakpoint in the Code View of App Designer. When the code execution pauses at the breakpoint, you can access the App's workspace using the command window. You can refer to the given link to understand how to set a breakpoint in a MATLAB code: https://www.mathworks.com/help/matlab/matlab_prog/set-breakpoints.html.

[collin bannister]

Hello Binaya,

Thanks for this idea! turns out I had one array that needed to be transposed!

I need to use this tool more often !

The only down side is it will not report out app. variables. do you know if there is a way to force it to show the app. variable states as well as the local variables?

Thanks

Answer 2

[Steven Lord]

Can you show us exactly how x and y are defined in your App Designer code? If you're retrieving them from a property of an edit box, are you using an EditField, a NumericEditField, or some other component? In particular what are the class of the x and y inputs with which you're calling polyfit?

x1 = [1 2 3];
class(x1)

ans = 'double'

x2 = '[1 2 3]';
class(x2)

ans = 'char'

y1 = [-2 -5 -9];
whos x1 y1 % same number of elements in x1 and y1

  Name      Size            Bytes  Class     Attributes

  x1        1x3                24  double              
  y1        1x3                24  double              

p1 = polyfit(x1, y1, 1) % works

p1 = 1x2

-3.5000 1.6667

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y2 = '[-2 -5 -9]';
whos x2 y2 % different sizes because different number of characters

  Name      Size            Bytes  Class    Attributes

  x2        1x7                14  char               
  y2        1x10               20  char               

p1 = polyfit(x2, y2, 1) % does not work

Error using polyfit (line 49)
The first two inputs must have the same number of elements.

If my suspicion is correct, that your x and y are text (char or string), you may want to switch to a NumericEditField.

[collin bannister]

Hello Steven,

shown here is the variables, the x and y are brought in through an excel (.csv) document that are converted to double type arrays

Note I added a little bit of context in the original post to add info about array manipulation before the poly fit function.

Thanks for the help!