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From: | Robert T. Short |
Subject: | Re: besseli: Am I missing something? |
Date: | Thu, 12 Jan 2012 06:16:17 -0800 |
User-agent: | Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.4) Gecko/20091017 SeaMonkey/2.0 |
Robert T. Short wrote:
Well, I will file the report. I will also make some tests for this and other cases.Before I file a bug report, maybe I should check that I am not all wet. If I recall my Bessel function theory, besseli(n,x) = besseli(-n,x) if n is an integer. In octave 3.4.2 I get octave:3> besseli(1,1),besseli(-1,1) ans = 0.565159103992485 ans = 0.565159103992485 Looks good for n=1, but for n=10 octave:4> besseli(10,1),besseli(-10,1) ans = 2.75294803983687e-10 ans = -1.40610343427994e-07 Not so good! And for n=100 octave:5> besseli(100,1),besseli(-100,1) ans = 8.47367400813812e-189 ans = 7.38028373423800e+170BTW, the numbers for positive n agree to about 9 or 10 decimal places with my tables. Also, BTW, the relationships for besselj seem to work fine.Anybody? Bob
I have already determined that the octave implementation is only good to maybe 9 places in other situations. Since Amos used asymptotic expansions in some cases, I can't imagine how we would get more, but I am not a numerical analysist. Since I am messing with this stuff, I will dig deeper and report back. Thanks for the comments and pointers.
Bob
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