On Wed, Aug 8, 2012 at 4:48 PM, Matthew Rocklin <[email protected]> wrote:
> Ah, I see. You want to substitute in monkey_log(whatever) for every > instance of log(whatever) in some expression. > > Yes. My goal here is to get back an mpf object. Ie., a number. > @sympy community - Do we have any technology to traverse the AST tree > and replace nodes with transformed nodes? > > SymPy has some basic pattern matching. I've never used it though. > Perhaps a combination of it and subs could help here? > > It looked to me that when it gets lambdified, it executes things in the namespaces with the provided aliases in the below file, so I should be able to include a namespace before mpmath that will be looked in first. Oddly, this worked before and it works on the second run of my code, but not the first (and not on this example). https://github.com/sympy/sympy/blob/master/sympy/utilities/lambdify.py#L194 > > On Wed, Aug 8, 2012 at 1:39 PM, Skipper Seabold <[email protected]> > wrote: > > On Wed, Aug 8, 2012 at 2:02 PM, Matthew Rocklin <[email protected]> > wrote: > >> > >> Would Piecewise work well here? > >> > >> > >> # Return 0 if x==0 else return log(x) > >> >>> monkey_log = Piecewise((0, Eq(x, 0)), (log(x), True)) > >> >>> fn = lambdify(x, monkey_log, 'mpmath') > >> >>> fn(0) > >> 0 > >> >>> fn(2.71828) > >> 0.999999327347282 > >> > > > > Maybe I'm being dense, but I'm not sure I understand correctly what to do > > with this. How do I inject this into the namespace used for evaluating > > lam_func in the below? I want to replace the log function which is part > of a > > bigger expression. > > > > Skipper > > > >> > >> > >> > >> On Wed, Aug 8, 2012 at 11:37 AM, Skipper Seabold <[email protected]> > >> wrote: > >>> > >>> Hi, > >>> > >>> I'm trying to evaluate a Hessian that I'm computing symbolically. To do > >>> so, I'd like to monkey-patch the mpmath.log function to define log(0) > == 0. > >>> I can replicate the error with the minimal example below. I get > >>> > >>> /usr/local/lib/python2.7/dist-packages/sympy/core/function.pyc in > >>> __new__(cls, *args, **options) > >>> 606 args = map(sympify, args) > >>> 607 result = super(AppliedUndef, cls).__new__(cls, *args, > >>> **options) > >>> --> 608 result.nargs = len(args) > >>> 609 return result > >>> 610 > >>> > >>> AttributeError: 'Float' object has no attribute 'nargs' > >>> > >>> > >>> However, what I'm seeing with my actual script is that the first time I > >>> run it, I get this error. The second time, it works, which is > baffling. I am > >>> on recent sympy master from git. Anyone have any ideas? Am I doing this > >>> wrong? > >>> > >>> import sympy > >>> from sympy.abc import y,x,z > >>> from sympy.utilities.lambdify import implemented_function > >>> from sympy import Function > >>> from mpmath import mpf, log as mplog > >>> > >>> func_ = y * sympy.log(x) * z > >>> func = func_(y, x).subs({z : 2.0}) > >>> > >>> log = implemented_function(Function("log"), lambda x : mpf(0) if x == 0 > >>> else mplog(x)) > >>> > >>> lam_func = sympy.lambdify((y, x), func, [{'log' : log}, 'mpmath']) > >>> > >>> data = (1., 2.) > >>> lam_func(*data) > >>> > >>> Thanks, > >>> > >>> Skipper > >>> > >>> -- > >>> 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. > > > > > > -- > > 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. > > -- 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.
