Question

I checked the answers about Lagrange interpolation, but I couldn’t find a suitable one to my question. I’m trying to use Lagrange interpolation for a surface with matlab. Let’s say I have a x and y vector and f=f(x,y). I want to interpolate this f function. I think, what I did is mathematically correct:

function q = laginterp(x,y,f,ff)

n = length(x);
m = length(y);
v = zeros(size(ff));
for k = 1:n
    for l = 1:m
        w1 = ones(size(ff));
        w2 = ones(size(ff))
        for j = [1:k-1 k+1:n]
            for j = [1:l-1 l+1:n]
                w1 = (x-x(j))./(x(k)-x(j)).*w1;
                w2 = (y-y(i))./(y(l)-y(i)).*w2;
            end
        end
        ff = ff + w1.*w2.*f(k,l);
    end
end

It is my function and then I’m waiting for an answer for any given x,y,f like

x= 0:4;
y = [-6 -3 -1 6];
f=[2 9 4 25 50];

v = laginterp(x,y,f,ff);
plot3(x,y,'o',f,q,'-')

I’m always grateful for any help!

Answer 1

This doesn’t address your question directly, but there’s a Lagrange interpolation function on the Matlab File Exchange which seems pretty popular.