Error using fittype for custom function

Hi I would like to fit a custom defined function (not continuous) to experimental time series data. My problem is that fittype does not accept my function although the function itself works fine and the syntax worked for similar functions. below you will find the fittype command I use, the error and the function that I would like to fit. Thank you in advance for any suggestions.

Lorenz

fittype command: ft1=fittype('Exp_delay_v2(t, tau1, tau2, a, b, dt1, dt2)','independent','t','coeff',{'tau1','tau2','a','b','dt1','dt2'});

Error using fittype>iCreateFittype (line 368) Expression Exp_delay_v2(t, tau1, tau2, a, b, dt1, dt2) is not a valid MATLAB expression, has non-scalar coefficients, or cannot be evaluated: Error in fittype expression ==> Exp_delay_v2(t, tau1, tau2, a, b, dt1, dt2) ??? Index exceeds matrix dimensions.

function y = Exp_delay_v2(t, tau1, tau2, a, b, dt1, dt2)

    y=zeros(size(t));

    s = 10.8*200;

    d1=dt1*200;
    d2=dt2*200;
    t1a = t(1:s-d2);
    t1b = t(s-d2+1:2*s-d2+d1);
    t2 = t(1:2*s-d1+d2);

        y(1:s+d1)    = ( (a+b) - b.*(1-exp(-(t1b)./tau2)) );
        y(s+1+d1:3*s+d2)   = (   a   + b.*(1-exp(-(t2)./tau1)) );
        y(3*s+d2+1:end) = ( (a+b) - b.*(1-exp(-(t1a)./tau2)) );

Answer 1

[Lorenz]

Solved the problem. fittype tests the function with only 2 independent input values, which causes an error in my custom function. I used a very untidy solution, by giving a default output if the size of the dependent variable is too short.

Thanks for looking anyway!

[Peter Reader]

Can you provide an exact solution to this? I have the same problem!

Answer 2

[ran]

Hi, I'm not sure I got what you meant. I want to have a custom function with many parameters, how should I do it?

[Lorenz]

I am not sure what you are looking for. Do you want to fit the parameters of the custom function? The documentation gives some good examples for that. Look for 'fit', 'custom function'. Lorenz