Status: Accepted
Owner: smichr
Labels: Type-Defect Priority-Medium
New issue 2092 by smichr: solve4linearsymbol should be hidden or fixed
http://code.google.com/p/sympy/issues/detail?id=2092
The only place that solve4linearsymbol is being used is in series/order and
its docstring and name suggest that it will solve for a linear symbol of
eqn == rhs. But since the use in order always sends a dummy var for rhs and
it only looks in eqn (not rhs) for the linear symbol it is essentially
behaving like rhs = 0. This leads to the incorrect behavior for the
following:
h[1] >>> from sympy.series.order import solve4linearsymbol as s
h[1] >>> s(x, 2-x)
(x, 2 - x)
It doesn't try to solve for x because it was written as a helper to order
which never sends an x-dependent expression for rhs.
Also, after differentiation, an expression linear in s should no longer
have s and there is no need to substitute in a value of s=0 into the
derivative (as is currently being done). Or am I missing something?
This function isn't in the namespace but it could be useful for doing what
it says...but it needs to then do what it says :-) I've got a commit in
github/smichr/1694cov that addresses and tests these issues. It's not up
for review but I'm just leaving a note that something has been done on it
there.
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