# gen_lengendre_p bug

Hi, wonder if someone here familiar with associated Legendre function can verify:

sage: gen_legendre_P(2, 2, x) 3*x^2 - 3

I think it should be

3 - 3*x^2

In Sage 8.9

Thanks

gen_lengendre_p bug

Hi, wonder if someone here familiar with associated Legendre function can verify:

sage: gen_legendre_P(2, 2, x) 3*x^2 - 3

I think it should be

3 - 3*x^2

In Sage 8.9

Thanks

add a comment

3

You are unfortunately facing a known issue, which is not solved yet:

https://trac.sagemath.org/ticket/25034

Associated Legendre functions and spherical harmonics in Sage require someone to work of them. Would you volunteer to do it?

**EDIT (17 May 2021)**: the bug has been fixed in SageMath 9.3 (released a week ago):

```
sage: gen_legendre_P(2, 2, x)
-3*x^2 + 3
```

0

Thanks, Eric_G. I am interested to help out. Is there a page with Sage volunteering process? I will sign up. I have computer science degrees but new to math (but seriously interested to learn).

Correct definition:

def legendre_function(l, m, f): return ((-1)^m * (1 - x^2)^(m/2) * diff(legendre_P(l, x), x, m)).subs(x = f) sage: legendre_function(2, 2, x) -3*x^2 + 3 sage: legendre_function(2, 2, cos(x)) -3*cos(x)^2 + 3

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Asked: ** 2020-02-12 18:40:28 +0100 **

Seen: **249 times**

Last updated: **May 17 '21**

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