Aaron S. Meurer wrote:
> You might want to look at the compare_ode_sol() (and the key
> equivalent rewrite I have at
> http://github.com/asmeurer/sympy/commit/2c5167990473ca4079f334214ffe0c898b18cbda).
> It is specifically for solutions given from dsolve(), but the
> heuristic involves seeing if the expression contains unevaluated
> Integral's, is or isn't solved for f(x), and finally, the length of
> str(expr).
>
> len(str(expr)) is probably the simplest way to check this. I never
> considered looking at the depth of the expression, though.
>
Currently I have just basic arithmetics, so I guess the heuristic would
reduce to len(str(expr)). That came to my mind earlier but I tried to
avoid that because computing str(expr) seems to be rather costly. My
experience is: printing the str representation of large expressions
(such as determinants) takes much more time than calculating them.
Just a (non representative) example: Computing that an expression has
"depth" 23 take less than a second. But computing str(expr) took too
long for my patience. (i.e. more than about 30 seconds)
For curiosity I did the following:
I used the function:
def count_branches(ex):
if ex.is_Atom:
return 1
else:
return sum(map(count_branches, ex.args))
to compute how many lowest level branches the tree has.
Result for my expression is 157130. (!)
The expression has many Rational-instances as atoms, so the average
stringlength of an atom in my case is 20. This means more than 2 MB of
str representation. When I relate this to the computation time of str(.)
of moderate expressions I get the feeling that this will take very long.
> By the way, you can probably make that operation faster first, by
> using the Poly class, and second, by somehow making det() do
> intermediate simplifications (things should actually already be
> better in this respect with the new polys).
Using the Poly class is a very good hint! In my first test speedup is
very notable.
But I really think intermediate simplifications are the key.
Unfortunately I have no idea how to do that.
But it is not that important at the moment.
I will concentrate on how I can avoid the complexity from the beginning.
Regards,
Bastian
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To post to this group, send email to sy...@googlegroups.com.
To unsubscribe from this group, send email to
sympy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sympy?hl=en.
