nlinfit using 3D coordinates

Hey guys! I'm trying to figure out this problem:

z(x, y) = A exp [−(((x − B)^2/2*C^2)+ ((y − D)^2/2*E^2))]

I'm given vector data for x,y, and z

So far I have tried using

fxn=@(C,x,y) C(1)*exp (−(((x − C(2))^2/2*C(3)^2)+ ((y − C(4))^2/2*C(5)^2)));

nlinfit(x,z,fxn,[3 3 3 3 3],[],y)

but I'm not sure how to pass the arguments through. HELP!!!

[E]

i guess I didn't write it, but I'm trying to fit the data using the given function..The only two things we have learned are polyfit and nlinfit so I know I have to use nlinfit

Answer 1

[Tom Lane]

I like your reasoning for using nlinfit.

I see two issues. First, use ".^" instead of "^" in your expression, because you want elementwise operations rather than matrix operations.

Second, nlinfit wants to call your function with the parameters as the first input and the X variables as the second. You have written a function that takes two different X variables as the second and third inputs. A simple way to deal with that would be to write a little converter:

otherfcn = @(C,xy) fxn(C,xy(:,1),xy(:,2));
nlinfit(x,z,otherfcn,[3 3 3 3 3])