Curve Fitting (polynomial fitting and interpolation)

Hello,

I am working on surface fitting of data. I am using "fit" function to perform polynomial fitting and interpolation for surface fitting. It is very sucessfull and i have no problem with it.

I have also used "griddata" for linear interpolation. This method is also very sucessfull.

While using "griddata", when i need to find the unknown z(z_req) from known x(x_req) and y(y_req), i use the below piece of code to do it :

x_req=0.8668;
y_req=0.1114;
z_req= griddata(xnew,ynew,znew,x_req,y_req,'linear');

it gives me the value for z , it is working fine.

Now i need to find the unknown z by using "fit" function, and i was not yet able to do it like i did with "griddata".

Is there any method to find the unknown z with the help of "fit" function in surface fitting?

[Matt J]

I am using "fit" function to perform polynomial fitting and interpolation for surface fitting.

Your terminology is confusing. Curve fitting and interpolation are different things.

Answer 1

[Matt J]

fit() will return a fitobject, which you can use to evaluate the surface at any point you wish

zq=fitobject(xq,yq)

It's important to understand that zq is is the value of the fitted surface at the point [xq,yq]. It is not an interpolated value, because the surface may not pass through the points you used to perform the fit.