Thanks. I think I understand what this code does. How do you want it
patched? Am I just writing my own alternative to sympy.latex? Are mainvar
and descending keyword arguments to sympy.latex or some other printing
function? I assume not everyone wants their polynomials in order of
descending powers or you guys would have already done this.
Ryan
On Mon, Jun 1, 2009 at 10:49 PM, Ondrej Certik <ond...@certik.cz> wrote:
>
> On Mon, Jun 1, 2009 at 9:33 PM, Ryan Krauss <ryanli...@gmail.com> wrote:
> > So, I think I have a good test and a better understanding of the problem:
> >
> > mylist = ['m', 's', 'b', 'x', 'y', 's', 'x', 'y', 's', 'EI']
> > sympy.var(mylist)
> > test = m*s**2+b*x*y*s+x**2+y**2+s+EI
> > args = list(test.args)
> > args.sort(sympy.Basic._compare_pretty)
> > args.reverse()
> >
> >
> > This doesn't get my list in the right order because of the number of
> > variables or whatever _compare_pretty does.
> >
> > It seems like I need to make a dictionary or something that uses the
> powers
> > of my main variable as the keys (this could cause issues if there is more
> > than one arg with the same power). What is the best way to sort based on
> > powers of the main variable? Is this the right approach:
> > args[1].as_coeff_exponent('s')
> >
> > (returns (y**2, 0) in this case) stepping through args in a for loop.
>
> I would just do it as I suggested above, e.g. like in
> sympy/core/basic.py:Basic._compare_pretty:
>
> @staticmethod
> def _compare_pretty(a, b):
> from sympy.series.order import Order
> if isinstance(a, Order) and not isinstance(b, Order):
> return 1
> if not isinstance(a, Order) and isinstance(b, Order):
> return -1
>
> # FIXME this produces wrong ordering for 1 and 0
> # e.g. the ordering will be 1 0 2 3 4 ...
> # because 1 = x^0, but 0 2 3 4 ... = x^1
> p1, p2, p3 = Wild("p1"), Wild("p2"), Wild("p3")
> r_a = a.match(p1 * p2**p3)
> r_b = b.match(p1 * p2**p3)
> if r_a is not None and r_b is not None:
> c = Basic.compare(r_a[p3], r_b[p3])
> if c!=0:
> return c
>
> return Basic.compare(a,b)
>
>
> So for example this code:
>
> from sympy import Wild, var, Basic
>
> mylist = ['m', 's', 'b', 'x', 'y', 's', 'x', 'y', 's', 'EI']
> var(mylist)
> test = m*s**2+b*x*y*s+x**2+y**2+s+EI
> args = list(test.args)
>
> def my_compare(a, b):
> main_var = s
> p1, p2, p3 = Wild("p1"), Wild("p2"), Wild("p3")
> r_a = a.match(p1 * s**p3)
> r_b = b.match(p1 * s**p3)
> if r_a is not None and r_b is not None:
> c = Basic.compare(r_a[p3], r_b[p3])
> if c!=0:
> return c
>
> return Basic._compare_pretty(a,b)
>
> print args
> args.sort(my_compare)
> print args
>
>
> produces:
>
> [m*s**2, b*s*x*y, y**2, s, EI, x**2]
> [EI, x**2, y**2, s, b*s*x*y, m*s**2]
>
>
> This should fix your problem. Please send a patch. :)
>
> Ondrej
>
> >
>
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