You're right. It seems to be a problem with equality checking. Here's some
code that I just ran:
In [3]: cs.theta == cs.phi
Out[3]: True
In [4]: cs.theta
Out[4]: cs.theta
In [5]: cs.phi
Out[5]: cs.phi
In [6]: id(cs.theta)
Out[6]: 169351684
In [7]: id(cs.phi)
Out[7]: 169350004
How come the == operator returns True even though the ids are different?
Also, I didn't implement __eq__ or __hash__ on BaseScalars.
Anyway, to reproduce the problem, you can run this (I'm just pasting from
my Ipython session):
In [1]: from sympy import *;from sympy.vector.vector import *;from
sympy.vector.integrate import *;q0, q1, q2 = symbols('q0 q1 q2');from
sympy.abc import x, y, z;c0 = CoordSysRect('c0');c1 = CoordSysRect('c1');cs
= CoordSysSph('cs')
In [2]: cs.theta * cs.phi
Out[2]: cs.theta**2
Should I implement __eq__ on BaseScalar?
(I probably won't be able to respond for 7-8 hours. Going to sleep. Have
classes tomorrow morning).
On Wednesday, August 28, 2013 10:17:39 PM UTC+5:30, Aaron Meurer wrote:
>
> On Wed, Aug 28, 2013 at 7:29 AM, Prasoon Shukla
> <[email protected] <javascript:>> wrote:
> > I have ran into a caching problem while working on my project for the
> vector
> > calcculus module. This occurred while I was debugging the express method
> on
> > vector (this isn't really relevant though).
> >
> > So, I have a symbol theta and another symbol phi.
> >
> >>>> cs.theta
> > cs.theta
> >
> >>>> cs.phi
> > cs.phi
> >
> > cs is an instance of the CoordSysSph class (again, not really relevant
> to
> > the problem at hand).
> >
> > The problem:
> >>>> sin(cs.theta) * sin(cs.phi)
> > sin(cs.theta) ** 2
> >
> > Well, in the definition for the cacheit decorator, the dicitionary
> > func_cache_it_cache exists. Now, when sin(cs.theta) is called, a key,
> value
> > pair gets added to the dictionary:
> >
> > ((sin, <class 'sympy.core.function.FunctionClass'>), (cs.theta, <class
> > 'sympy.vector.vector.BaseScalar'>)) : sin(cs.theta)
> >
> > Now, when SymPy needs to calculate sin(cs.phi), the cacheit decorator is
> > called again. The lookup key for sin(cs.phi) is generated as:
> > ((sin, <class 'sympy.core.function.FunctionClass'>), (cs.phi, <class
> > 'sympy.vector.vector.BaseScalar'>))
>
> Oh, just noticed this. phi and theta are not Symbols, they are
> BaseScalars. So you probably did something wrong implementing equality
> comparison on BaseScalars. What does "cs.phi == cs.theta" give?
>
> Can you give a complete code snipped to reproduce this in your branch?
>
> Aaron Meurer
>
> >
> > At this point, the func_cache_it_cache does not have the key
> correspondind
> > to sin(cs.phi), as it shouldn't. But, here's the catch: running the
> has_key
> > method on func_cache_it_cache for this second key (for sin(cs.phi))
> returns
> > True. That means, the cache returns sin(cs.theta). And that is what is
> > causing the problem.
> >
> > What can I possibly do here? For the time being, I am going to proceed
> with
> > the debugging. When there is a solution for this problem, we can go
> ahead
> > and fix this.
> >
> > --
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