On Sat, Jun 30, 2012 at 7:48 PM, Aaron Meurer <[email protected]> wrote: > On Jun 30, 2012, at 8:38 PM, "[email protected]" > <[email protected]> wrote: > >> Two reasons basically: >> >> - the original lambdify has a very convoluted logic and seems hard to >> maintain (the new one is not that great either, however it does not >> break as easily) (in the commit history one can see how stuff >> completely unrelated to the functionality of lambdify was bolted on >> it) >> >> - there were serious differences between what the docstring says and >> what lambdify does in many corner cases >> >> I have discussed a lot why I dislike the original lambdify back in >> November when I was writing the plotting module. I can bring these >> discussions back if there is interest. I have also documented this in >> details at the beginning of the source file for the new lambdify. It >> would be nice to merge them together, but there is too much cruft in >> the old lambdify so this will be difficult (even useless, I would >> prefer simply removing both lambdify functions and relying on good >> code in sympy for performance, not on some strange combination of >> libraries and eval(str) operations) > > +1 to this. Each function should know how to numerically evaluate > itself using numpy or stdlib math (or whatever), and you should be > able to just do it directly, like expr.evalf(library=numpy) or > something like that. I don't see any reason why that wouldn't work. > eval'ing strings feels like a hack, but actually imo anything that > works by rebuilding the expression tree in some what or another is > inefficient because we already have the expression tree.
The idea is quite simple. In SymPy, sin(x)+cos(x) is equivalent to Add(sin(x), cos(x)) and so if you need to evaluate it at x=5, you need to run a couple function calls, recursively, and finally you just call math.sin or math.cos from the Python's math module. Using Python's math module directly, sin(x)+cos(x) is just two function calls and a "+" on two floats. So it is much faster. How can this be done without lambdify()? ------------------ Stefan, yes, I read the module introduction, but it was not clear to me at all what the difference is. The description sounds like a temporary hack. But from what you are saying, it seems to me it's a better implementation of lambdify(). I agree with you that the best would be to simply rely on sympy directly, but I don't know how to do that. Ondrej -- 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.
