'poly1' unrecognized

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Igor on 11 May 2023
Commented: Walter Roberson on 12 May 2023
Dear all
I am trying to to a fit to simple polynomial function.
However, when I try to use 'poly1' as a fittype it gives: Unrecognized function or variable 'poly1'.
I am using the command form as in the library f = fit(x, y, 'poly1'), or f = fit(x, y, poly1) -nothing works
how is it possible? I though it should be in the library as written here:
thank you

Answers (1)

Chunru on 11 May 2023
x = (0:0.2:5)';
y = 2*exp(-.2*x) + 0.5 * randn(size(x));
f = fit(x, y, 'poly1');
% check the path of fit
which fit
plot(f, x, y)
% f = fit(x, y, poly1) % not working unless poly1='poly1';
Walter Roberson
Walter Roberson on 12 May 2023
which fit
asks MATLAB to first search the workspace (and calling parameters, and any shared variables) to see whether the name fit is associated with a variable in scope, and if so then tells you that it is a variable. If fit is not found as a variable in scope, then MATLAB searches for functions named fit, and if one is found then MATLAB will tell you the path to the function that was found.
Note that the search will not necessarily find the same fit that a call to fit will resolve to. If the parameters to fit involve a class that defines a method named fit then which fit will not find that method. You can, however, ask for (for example)
which fit(x)
in which case MATLAB will search for the fit that would be called if a value with the same type as x were to be passed to fit

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