n = 100;

% non-trivial case
x = linspace(0,1,n).^2;
y = linspace(0,1,n).^2;
z = linspace(0,1,n).^2;

[X,Y,Z] = ndgrid(x,y,z);

% number of points to interpolate

m = 1000000;

xi = linspace(0,1,m);
yi = linspace(0,1,m);
zi = linspace(0,1,m);

F = sin(3*X) .* cos(2*Y) .* sin(4*Z);


tic
fi = interpn(X,Y,Z,F,xi,yi,zi);
toc

% check sum
mean(fi)