evaluate curve fit sum of sine

Good evening,

I am having troubles in evaluating my curve fitting using the sum of sines methot, as it best suits my datas.

I have read the related page that prompts by typing doc cfit, but it seems to be relatend only with polynomial curve fitting.

Basically I need to have something to input in another function, to evaluate P(t).

I'have tried to copy the general model with the given coefficients and replace x with a t vector from 0 to 1.4 in order to do so, but it seems not to work.

What am I doing wrong?

Is there a quicker/easier way to do so?

Thanks for your help!

Answer 1

[Matt J]

The cfit object returned by fit() can be used as a function handle, to evaluate the fitted function at any desired query points.

load enso;
f = fit( month, pressure, 'sin6');
y=f(50), %evaluate at t=50

y = 10.8555

So, you can just pass f around to any code that needs to query the fit.

[Giulio Rossi]

thanks for you help!

the problem is that when i try to multiply the function f ( in my case is a time dependant function), matlab prompts

Undefined operator '*' for input arguments of type 'cfit'.

how can I solve this?

[Matt J]

You cannot perform multiplications with a fit object, but you can multiply with values returned by a fit object, e.g.,

load enso;
f = fit( month, pressure, 'sin6');

y=f(1:10).',

y = 1×10

12.4425 12.3078 11.4515 10.2027 8.9859 8.2036 8.1253 8.8129 10.1047 11.6591

ytimes10  =  10*f(1:10).'

ytimes10 = 1×10

124.4250 123.0784 114.5152 102.0265 89.8588 82.0364 81.2526 88.1293 101.0474 116.5914