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Substitute equation into another one

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Moritz on 31 Oct 2012
I'm wondering whether there is a neat way to substitute an equation into another one.
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


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Accepted Answer

Argon on 31 Oct 2012
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...

  1 Comment

Moritz on 31 Oct 2012
So simple and so brilliant. Looks like I couldn't see the forest for the trees... Thanks a lot!

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