On Jan 19, 2012, at 10:58 AM, Vinzenz <[email protected]> wrote: > Hi, > since I can't post to the thread > http://groups.google.com/group/sympy/browse_thread/thread/135ed5dc84d87dd5/18b2d34a997b3139?#18b2d34a997b3139 > anymore, here is a summary/continuation of the discussion: > > Thank you very much for your help. > > I have a differential equation such as > ddq = B^-1(q) * ( T - rest(q,dq)) > which I want to numerically evaluate > where ddq is a 7x1 sympy matrix, B 7x7 (can not invert it symbolically > anymore) and q, dq are the supplied input variables. > > So far I used lambdify successfully with ddq (2x1), B (2x2) (can > invert sym.). > > To summarize (correct me if I'm wrong / sth. missing) and current > states: > - symbolic simplification has been primarily discussed. (I will open a > new thread for this) > - expand + rewrite(exp) + expand + rewrite(cos) works but takes > too much memory for larger expressions (especially the 2nd expand) > - with disabled cache it uses much less memory but becomes too > slow > - my calculations are done in sympy, but I export to Mathematica, > simplify, and reimport to sympy at the moment > - I also tried the improved trigsimp which has been posted to the > mailing list recently (was not more successful) > - cse is an option > - there were problems with solve (in which repo is your version, > smichr?) and chop (I use the function you supplied) > > To get back to the original topic (Numerical Evaluation): > - I want to use results I obtained with sympy for simulations using > scipy's ode integrators. > A fast numerical evaluation is therefore desireable. > It would be nice to save the conversion results accross program > executions. > - is it a good idea to use lambdify for large matrices? > - it is quite slow and since I get a function I can't pickle > it, it has to be done each run > - what about generating a py file with function evaluating the > expression with numpy? > - afaik, lambdify replaces functions / operators for e.g. > numpy. could one get the actual expression (to save it, make a > module)? > - what about evalf(var1=1234.....)? > - what about using autowrap / binary_function? > - see e.g. > http://ojensen.wordpress.com/2010/08/10/fast-ufunc-ish-hydrogen-solutions/ > .I got the example working, but I am not sure if this would help me > (element-wise application) > - What about http://code.google.com/p/numexpr/ ? What would be a > way to convert my sympy expressions so they can be evaluated with > numexpr > > I appreciate if you could comment and share your experiences regarding > similar problems. > > Vinzenz > > > PS: Google Groups is funny, hides the list answer buttons without any > hint. @Chris Smith: Sorry for writing directly to you. Also, google > search does not show messages from this mailing list, but 3rd party > sites (which also show the complete mail addresses). >
I guess they're just trying to keep people from resurrecting old threads. Or else there is just a bug. If you read and reply to messages in your email client, you can always reply to old threads at any time. Aaron Meurer > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
