Hi there, I got a set of discrete Data as functions of 4 variables (x1,x2,x3,x4) . I would like to interpolate the data and then get a continuous function f in terms of (x1,x2,x3,x4). Finally I would like to get the partial derivative of f wrt x2. How can I sort out this? x0:= 1/2: s:=x->x^2: sol:=(x2,x3,x4)->dsolve({y''(x1)-(x3^2+s(x1)*x4^2)*y(x1)=0,y(x2)=exp(-x2),y'(x2)=1/2},numeric,output=operator,range=0..x0): g:=(x1,x2,x3,x4)->eval(y(x1),sol(x2,x3,x4)): g(x0/3,x0/3,10,1); dx2:=1/1000: Data:=(x1,x2,x3,x4)->[seq([x2+i*dx2,g(x1,x2+i*dx2,x3,x4)],i=-3..3)]: ???