It should work with a custom dictionary. At the very least, it will
work with any iterator or (old, new) pairs.
You could also make f symbolic and unevaluated by default, then call
doit after the substitution. It won't be 100% efficient if the same f
will appear more than once, though.
Aaron Meurer
On Apr 27, 2013, at 10:51 AM, Alan Bromborsky <abro...@verizon.net> wrote:
> On 04/27/2013 12:40 PM, Alan Bromborsky wrote:
>> consider the sympy expressions -
>>
>> a = a_1*e_1+...+a_n*e_n
>>
>> b = b_1*e_1+...+b_n*e_n
>>
>> where the a_i's and the b_i's are commutative sympy expressions and the
>> e_i's are non-commutative symbols and you have a dictionary
>>
>> mul_dict = {e_i*e_j: f(e_i,e_j)}
>>
>> if mul_dict is fully populated then
>>
>> a*b = (a*b).subs(mul_dict)
>>
>> However many of the entries in the dictionary will never be used since most
>> of
>> the a_i's and b_i's will be zero, but you don't know which ones ahead of the
>> multiplication.
>>
>> Likewise the function f(e_i,e_j) is know but time consuming to evaluate.
>>
>> Is there a way to do a subsitution in a sympy expression where if e_i*e_j is
>> a key subs will use
>> the dictionary, but is e_i*e_j is not a key f(e_i,e_j) will be evaluated,
>> added to the dictionary, and
>> the substitution performed?
> I guess the real question is is there a way of use a custom dictionary class
> Mydict(dict) with the sympy
> subs operation?
>
> --
> You received this message because you are subscribed to the Google Groups
> "sympy" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to sympy+unsubscr...@googlegroups.com.
> To post to this group, send email to sympy@googlegroups.com.
> Visit this group at http://groups.google.com/group/sympy?hl=en-US.
> For more options, visit https://groups.google.com/groups/opt_out.
>
>
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sympy+unsubscr...@googlegroups.com.
To post to this group, send email to sympy@googlegroups.com.
Visit this group at http://groups.google.com/group/sympy?hl=en-US.
For more options, visit https://groups.google.com/groups/opt_out.
