code review 217060: math: add lgamma; in-line special cases of acosh, nextafter

math: add lgamma; in-line special cases of acosh, nextafter

Added lgamma.go, tests and special cases.

[Charlie Dorian, 2010-02-20 04:14:45]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change.

[Charlie Dorian, 2010-02-20 05:29:39]

Hello rsc (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2010-02-22 22:45:25]

http://codereview.appspot.com/217060/diff/13/17
File src/pkg/math/lgamma.go (right):

http://codereview.appspot.com/217060/diff/13/17#newcode91
src/pkg/math/lgamma.go:91: // Lgamma returns the natural logarithm of the Gamma
function
// Lgamma returns the natural logarithm and sign of Gamma(x).
// The sign is -1 or +1 except in the special cases.

or

// Lgamma returns the natural logarithm and sign (-1 or +1) of Gamma(x).

depending on whether NaN gets sign == 0.

http://codereview.appspot.com/217060/diff/13/17#newcode100
src/pkg/math/lgamma.go:100: func Lgamma(x float64) (lgamma float64, signgam int)
{
signgam is an awkward variable name.
I suggest renaming sign below to neg and
renaming signgam to sign.

[Charlie Dorian, 2010-02-23 01:07:25]

Hello rsc (cc: golang-dev@googlegroups.com),

Please take another look.

[Charlie Dorian, 2010-02-23 01:07:37]

Thanks.

On Mon, Feb 22, 2010 at 5:45 PM, <rsc@golang.org> wrote:

>
> http://codereview.appspot.com/217060/diff/13/17
> File src/pkg/math/lgamma.go (right):
>
> http://codereview.appspot.com/217060/diff/13/17#newcode91
> src/pkg/math/lgamma.go:91: // Lgamma returns the natural logarithm of
> the Gamma function
> // Lgamma returns the natural logarithm and sign of Gamma(x).
> // The sign is -1 or +1 except in the special cases.
>
> or
>
> // Lgamma returns the natural logarithm and sign (-1 or +1) of Gamma(x).
>
> depending on whether NaN gets sign == 0.
>

Changed comment to second choice.  That way Gamma(x) = sign*Exp(Lgamma(x))
is correct for any value of x.

>
> http://codereview.appspot.com/217060/diff/13/17#newcode100
> src/pkg/math/lgamma.go:100: func Lgamma(x float64) (lgamma float64,
> signgam int) {
> signgam is an awkward variable name.
> I suggest renaming sign below to neg and
> renaming signgam to sign.


Done.

(When I add Gamma(x) to the math package, I think it should be just Gamma(x)
rather than Tgamma(x).  Go doesn't have the same history as C.)

>
>
> http://codereview.appspot.com/217060/show
>

[rsc, 2010-02-23 01:11:55]

LGTM

[rsc, 2010-02-23 01:12:51]

*** Submitted as http://code.google.com/p/go/source/detail?r=d6550a79bfef ***

math: add lgamma; in-line special cases of acosh, nextafter

Added lgamma.go, tests and special cases.

R=rsc
CC=golang-dev
http://codereview.appspot.com/217060

Committer: Russ Cox <rsc@golang.org>