programmatically determining the terms in an expression

[Nathan Thern]

I have performed a long series of symbolic calculations to arrive at an expression:

(xaa*(-λaa - λab + 1) - xaa + xab*λaa + xac*λab)
/
sqrt((-xaa*(-λaa - λab + 1) - xab*λaa - xac*λab + xba*(-λba - λbb + 1) + xbb*λba + xbc*λbb)**2 +
     (-yaa*(-λaa - λab + 1) - yab*λaa - yac*λab + yba*(-λba - λbb + 1) + ybb*λba + ybc*λbb)**2 +
     (-zaa*(-λaa - λab + 1) - zab*λaa - zac*λab + zba*(-λba - λbb + 1) + zbb*λba + zbc*λbb)**2)

which is of the form

(F*λab + G)/sqrt(A*λab**2 + B*λab + C)

Given the input, how do I assign the right expressions to A,B,C,F & G?

This seems like a common theme for a newbie question, and I'm sorry if it's been asked before; but I couldn't find anything in this list that helped me. I'd rather have a few hints or pointers to the right place in the manual than a complete solution.

thanks,

NT

[Nathan Thern]

Actually, I think I can do it with the args property. If I'm not on the right track, someone let me know.

I'm still figuring out how I can determine the power terms

[Nathan Thern]

OK,

Poly(expr.args[0].args[0],λab).coeffs()

gets me the A, B & C coefficients inside the square root.

Sorry if I wasted everyone's time, but I'm going to leave the post here in case it helps someone else out.

[Aaron Meurer]

I think you are looking for pattern matching.
http://docs.sympy.org/dev/modules/core.html#sympy.core.basic.Basic.match

Aaron Meurer

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