Substitute equation into another one

Hi,

I'm wondering whether there is a neat way to substitute an equation into another one.

Example:

1st equation: x*dx*dy+dy*dz*x+z

2nd equation: dx+dz=u

Expected solution: x*dy*u+z

How do I do that? Right now I wrote a script, which can do it (but its 70 lines long and quite slow). Is there an easy solution?

Thank you very much!

Product: Matlab 2012a

Answer 1

[Argon]

Like that?

f = sym('x*dx*dy+dy*dz*x+z');
g = sym('dx+dz=u');

simplify(subs(f, 'dx', solve(g, 'dx')))

Of course, it gets harder if your equation is non-linear...

[Moritz]

So simple and so brilliant. Looks like I couldn't see the forest for the trees... Thanks a lot!