Comment #26 on issue 3148 by trel...@yahoo.com: Too many constants from
dsolve()
http://code.google.com/p/sympy/issues/detail?id=3148
I now have a candidate branch that manages constants better.
https://github.com/zanzibar7/sympy/tree/dsolve_fixes_pullable
Example:
dsolve((x+1)*f(x).diff(x) - f(x)- 1,f(x))
f(x) = C₁ x + C₁ - 1
The general problem of constant simplification is hard. My intution tells
me it's analogous to the Boolean satisfiability problem, which is NP
complete in the general case. So rather than trying to exhaustively
simplify constants, this new version performs a few very shallow
simplifications and stops there. The up-side is that constant
simplification runs relatively fast.
While this does the job for now, this probably won't close the book for
good. May of the ode tests expect solutions to be in a particular
arbitrary form. Changes and improvements to dsolve() in the future may
cause tests to fail even though correct solutions are still returned. In
addition, there are a few spots where the solution
form depends on poorly defined functions like collect() which can have
un-intended side-effects on the simplification process.
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