'poly1' unrecognized

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:

https://uk.mathworks.com/help/curvefit/list-of-library-models-for-curve-and-surface-fitting.html#btbcvnl

thank you

Answer 1

[Chunru]

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

/MATLAB/toolbox/curvefit/curvefit/fit.m

plot(f, x, y)

% f = fit(x, y, poly1)  % not working unless poly1='poly1';

[Igor]

thank you very much for the answer.

I just dont understand why then f = fit(x, y, 'poly1') didnt work for me f = fit(x, y, 'poly1'); works

[Torsten]

Did you name one of your MATLAB functions "fit.m". Then rename it.

What does

which fit

give as output ?

Do you have the curve fitting toolbox installed and licenced ?

[Igor]

Hi

thank you for answer, yes I actually names the script file as fit.m so that could cause problems.

I think I have curve fitting toolbow add.

What is the function of - which fit?

[Walter Roberson]

@Igor

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