Ask Your Question
1

A bug in Laguerre-L?

asked 2014-10-21 23:54:59 +0200

Peter Luschny gravatar image

updated 2014-10-22 13:02:02 +0200

laguerre(-1,1) returns 0 in Sage but returns exp(1) in Maple and Mathematica.

The docs say: "Return the Laguerre polynomial for integers n>−1."

Is this expected behaviour to return an innocent value instead of giving the user a warning?

Edit: I give an example how this behaviour can bite: Look at the Inverse Lah transform of 1,2,3,... which starts 1, -2, -1, 2, 17, 94, 487, ... This can be computed by

factorial(n)*(laguerre(n,1)-2*laguerre(n-1,1))

This expression gives for n=0 the expected value '1' and thus hides the fact that the formula is true only for n>0!

edit retag flag offensive close merge delete

1 Answer

Sort by » oldest newest most voted
2

answered 2014-10-22 02:23:28 +0200

kcrisman gravatar image

Great point. Those orthogonal polynomials haven't had much TLC for a long time. I've opened http://trac.sagemath.org/ticket/17192 for this.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower

Stats

Asked: 2014-10-21 23:54:59 +0200

Seen: 126 times

Last updated: Oct 22 '14