On 2013-03-30, tvn <[email protected]> wrote:
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> In sympy there's a method call as_coeffficients_dict() that returns all
> the terms and their coefficients from an expression. I am if I can do
> something like this in Sage.
you can do a similar thing, except that the monomials are encoded by
their exponents
sage: R.<x,a> = ZZ[]
sage: p=x^2*a-a^2+a-4
sage: p.dict()
{(0, 0): -4, (0, 1): 1, (0, 2): -1, (2, 1): 1}
sage:
That is, each term "(i,j): t" corresponds to monimial
x^i a^j having non-zero coefficient t.
The conversion is easy, by getting the variables of p as follows:
sage: p.variables()
(x, a)
For examples
>
>
>
> >>> (3*x + a*x + 4).as_coefficients_dict()
> {1: 4, x: 3, a*x: 1}
>
> >>> (3*a*x).as_coefficients_dict()
> {a*x: 3}
>
> >>> (x-oo).as_coefficients_dict() #can also deal with infinity
> {1: -oo, x: 1}
>
>
>
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