Hi. I know the title is not very informative. Here's what I'm trying to do: I have f(x,y). I want to perform a change of variables to obtain a pre-defined g(u,v). How can I work out the actual expressions u(x,y) and v(x,y) so that it works out (including the Jacobian as well)? I have a vague feeling that there may not be a general approach but only techniques for specific forms of f and g. I have Googled and searched for "change of variables" on this forum. 9 pages later, I think no one has asked this before. Some directions (even Google keywords) would be much appreciated.