On Mar 26, 2013, at 6:38 PM, Duane Nykamp <[email protected]> wrote:
Thanks for the suggestions.
I ended up with
class deferred_gcd(Function):
nargs = 2
def doit(self, **hints):
if hints.get('deep', True):
return sympy.gcd(self.args[0].doit(**hints),
self.args[1].doit(**hints))
else:
return sympy.gcd(self.args[0], self.args[1])
Using this same idea, I was able to create a deferred min/max, though I
limited it to two arguments, as I'm not sure how to use map to apply .doit
to all arguments.
Max(*[i.doit(**hints) for i in self.args])
And use Max, not max (the SymPy version properly handles incomparable
things).
class deferred_max(Function):
nargs = 2
def doit(self, **hints):
if hints.get('deep',True):
return max(self.args[0].doit(**hints),
self.args[1].doit(**hints))
else:
return max(self.args[0], self.args[1])
It doesn't seem like sympy consistently employs the "deep" hint. For
example, I couldn't get the sympy sign function to propagate doit to its
argument as it doesn't have the **hints argument. I wanted to use
sign(max(a,b)) and have sign pass .doit to the deferred max. Since I
couldn't get it to work, I just made a deferred_sign function of the above
form. It seems to work fine.
Yes, doit should be rewritten like expand to handle deep processing
automatically.
Aaron Meurer
Thanks,
Duane
On Tuesday, March 26, 2013 3:18:13 PM UTC-5, Mateusz Paprocki wrote:
>
> Hi,
>
> On 26 March 2013 21:00, Duane Nykamp <[email protected] <javascript:>>
> wrote:
> > I'd like to delay evaluation of functions like gcd so that I can have
> users
> > enter an expression like gcd(a,b), where a and b will be replaced by
> > numbers. If I just enter gcd(a,b), it finds the gcd of the polynomials
> a
> > and b, which is one. Based on earlier feedback I receive here and by
> trial
> > and error, I came up with this method to delay evaluation, and I'm just
> > wondering if this is a reasonable way to do it. I can't say I really
> > understand the difference between subs and replace. I just messed
> around
> > until I found a method that worked.
> >
> > For example, if a and b are eventually going to be 3 and 9, the
> following
> > seems to work correctly, giving 3. I'm using parse_expr, as the
> expressions
> > are entered in a web page.
> >
> > In [170]: parse_expr('gcd(a,b)',local_dict={'gcd':
> >
> Function('gcd')}).subs([(Symbol('a'),3),(Symbol('b'),9)]).replace(Function('gcd'),gcd)
>
> > Out[170]: 3
> >
> > Is this a reasonable approach? Or is there a better method?
> >
>
> You can use this:
>
> In [4]: class gcd(Function):
> ...: @classmethod
> ...: def eval(cls, x, y):
> ...: if x.is_Number and y.is_Number:
> ...: return x.gcd(y)
> ...: else:
> ...: return None
> ...:
>
> In [5]:
>
> In [5]: var('a,b')
> Out[5]: (a, b)
>
> In [6]: gcd(a, b)
> Out[6]: gcd(a, b)
>
> In [7]: _.subs(a, 12)
> Out[7]: gcd(12, b)
>
> In [8]: _.subs(b, 6)
> Out[8]: 6
>
> > Thanks,
> > Duane
> >
> > --
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> >
> >
>
> Mateusz
>
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