Error using polyfit (line 44) The first two inputs must have the same number of elements

I don't see where is the problem.

function PolynomeButtonPushed(app, event)
            fct = app.LafonctionEditField.Value;
            I = linspace(app.MinEditField.Value,app.MaxEditField.Value,app.NombredespointsEditField.Value);
            n = app.LodredupolynomeEditField;
            
            polynome = polyfit(I,fct,n);
            app.EditField.Value = polynome;
        end
    end

Answer 1

[Matt J]

The error message has given you a big clue to where the problem is. Did you examine/verify the contents of I and fct to see if they have the same length?

[Youssef Aberkane]

[Steven Lord]

If app.LafonctionEditField is the box where you've entered sin(x+1), how long is that value?

s = 'sin(x+1)'

s = 'sin(x+1)'

strlength(s)

ans = 8

The text sin(x+1) does contain 8 characters. It does not somehow deduce that you want this to be a function evaluated at some set of points x (which is not defined in the callback function.) If you want that to be a function that you can evaluate for a specific array of values x, turn it into a function handle.

fh = str2func("@(x)" + s)

fh = function_handle with value:
    @(x)sin(x+1)

functionValues = fh(0:5)

functionValues = 1×6

0.8415 0.9093 0.1411 -0.7568 -0.9589 -0.2794

[Youssef Aberkane]

I change fct = app.LafonctionEditField.Value; with fh = str2func("@(x)" + s) ??

[Steven Lord]

That makes a function handle. Now if you want to do something with it, you should evaluate it like I did when I created the variable functionValues.

[Youssef Aberkane]

What should I change ?

function PolynomeButtonPushed(app, event)
            s = app.LafonctionEditField.Value;
            fct = str2func("@x" + s);
            I = linspace(app.MinEditField.Value,app.MaxEditField.Value,app.NombredespointsEditField.Value);
            n = app.LodredupolynomeEditField;
            
            polynome = polyfit(I,fct,n);
            app.EditField.Value = polynome;
        end
    end

[Torsten]

fct = str2func("@(x)" + s);
polynome = polyfit(I,fct(I),n);

[Youssef Aberkane]

Same error

[Matt J]

polynome = polyfit(I,fct(I),n);

Answer 2

[Matt J]

Take a look at this.

[Youssef Aberkane]

didn't help

[Torsten]

If you use the following code, what is written to screen ?

function PolynomeButtonPushed(app, event)
  s = app.LafonctionEditField.Value;
  fct = str2func("@(x)" + s);
  disp(fct)
  disp(class(fct))
  I = linspace(app.MinEditField.Value,app.MaxEditField.Value,app.NombredespointsEditField.Value);
  disp(I)
  disp(class(I))
  n = app.LodredupolynomeEditField;
  disp(n)
  disp(class(n))
  pause()
  polynome = polyfit(I,fct(I),n);
  app.EditField.Value = polynome;
end

[Youssef Aberkane]

there is no errors but its doens't shows the result of polyfit

[Torsten]

What does it show for fct, I and n ?

[Youssef Aberkane]

i had a bug so i restarted my laptop when i run the code this error pops up

[Torsten]

Is it not possible that you just report the six outputs of the function written to screen (I added three in the code) ?

As far as I can see, "n" is not of class "double", but of class "matlab.ui.control.NumericEditField". This produces one error in polyfit. Do you know how to convert "n" to type "double" ? Most probably, n=double(n) should do in your code. Or use "cast". And most probably, the same is necessary for I.