Could anyone suggest a solution for this? I can make a list of
substitutions by hand (as below) and pass that to the .subs() method, but
surely there is a better way.
s_list={
Abs(a - 1) : S(1) - a,
Abs(a - 2) : S(2) - a,
Abs(2*a - 3) : S(3) - S(2)*a,
Abs(a**2 - 2) : S(2) - a**2,
Abs(a**2 - 3) : S(3) - a**2,
Abs(a**2 - 11) : S(11) - a**2,
Abs(2*a**2 - 1) : S(1) - S(2)*a**2,
Abs(2*a**2 - 3) : S(3) - S(2)*a**2,
Abs(3*a**2 - 2) : S(2) - S(3)*a**2,
Abs(3*a**2 - 16) : S(16) - S(3)*a**2,
Abs(4*a**2 - 3) : S(3) - S(4)*a**2,
Abs(5*a**2 - 4) : S(4) - S(5)*a**2,
Abs(5*a**2 - 7) : S(7) - S(5)*a**2,
Abs(5*a**2 - 16) : S(16) - S(5)*a**2,
...
}
On Sunday, March 28, 2021 at 11:14:57 AM UTC+2 B A wrote:
> I am a sympy beginner, and fairly new to python, so I suspect that my
> question has a simple answer, but have not been able to figure it out
> myself.
>
> I have sympy expressions containing the built-in Abs function. The
> arguments of Abs() are polynomials in a=symbol('a',
> real=True,positive=True) . Here are a three examples:
>
> Abs(a**2 + 2)
> sqrt(2)*Abs(2*a**2 - 1)/3
> sqrt(2)*(a + 1)*Abs(a - 1)/3
>
> Here's the point: I know that 'a' is approximately 0.6. So in cases where
> the argument of Abs has an unambiguous sign (within floating-point
> precision) I would like to simplify the absolute value. For example in the
> three cases above I would like:
>
> Abs(a**2 + 2) -> a**2 + 2
> sqrt(2)*Abs(2*a**2 - 1)/3 -> sqrt(2)*(1- 2*a**2)/3
> sqrt(2)*(a + 1)*Abs(a - 1)/3 -> sqrt(2)*(a + 1)*(1-a)/3
>
> where the right arrow '->' indicates replacement or simplification. Note
> the change of sign in the second and third examples, because (for example)
> I know that (a-1) is negative.
>
> Is there a (simple) way to implement this?
>
> Thank you!
> Bruce
>
--
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 [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/sympy/253c3643-71e4-4073-9134-ac53f2b7f605n%40googlegroups.com.
