Updates:
        Labels: EasyToFix

Comment #7 on issue 1696 by [email protected]: integral of heaviside
http://code.google.com/p/sympy/issues/detail?id=1696

But an algorithm to convert general piecewise expressions to use Heaviside would be very useful. Because usually, integrate() has a better chance of integrating Heaviside than Piecewise (especially if the limits are infinite, or if the integral is indefinite).

Actually, a better thing to do would be to add something that should have been added a long time ago, a special derivative for heurisch. This way, we could define Heaviside(x).heurisch_diff(x) to be 0 for heurisch, but keep Heaviside(x).diff(x) as DiracDelta(x). As I noted above, heurisch just needs to know what the derivative is in terms of the function itself to work. This would also let us do things like change tan(x).diff(x) to the more common sec(x)**2, but still make integrals in terms of tan(x) work.

This would be easy to implement. Just add a new method heurisch_diff() to these functions, and check if it is defined and use it in heurisch instead of diff. Probably we should use a better name than that, since it could be useful outside of heurisch too (in particular, in other integration algorithms).



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