% fun_gradient.m — Surface gradient of a scalar function.
%
% grad differentiates a surfacefun, automatically accounting for the
% on-surface metric. It returns the three Cartesian components of the
% surface gradient.

mip load --install flatironinstitute/flatironinstitute/surfacefun

p = 16;
nref = 2;
dom = surfacemesh.sphere(p + 1, nref);

f = surfacefun(@(x, y, z) cos(6*x) .* y + exp(z), dom);

[fx, fy, fz] = grad(f);

figure(1);
subplot(131), plot(fx), title('\partial_x f')
subplot(132), plot(fy), title('\partial_y f')
subplot(133), plot(fz), title('\partial_z f')