can anyone please explain me this code ..exactly whats happening here while computing curvature ?

function k = curvature_central(u)

% compute curvature

[ux,uy] = gradient(u);

normDu = sqrt(ux.^2+uy.^2+1e-10);

Nx = ux./normDu;

Ny = uy./normDu;

[nxx,junk] = gradient(Nx);

[junk,nyy] = gradient(Ny);

k = nxx+nyy;