From bug-request at octave dot org Tue Nov 15 12:26:46 2005
Subject: Inverse Trigonometric Functions (in degrees)
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: William Poetra Yoga H <williampoetra at yahoo dot com>
Cc: bug at octave dot org
Date: Tue, 15 Nov 2005 13:26:39 -0500

On 15-Nov-2005, William Poetra Yoga H wrote:

| function retval = acosd (x)
| 
|   if (nargin != 1)
|     usage("acosd (x)");
|   end
| 
|   x(find(x == inf)) = NaN;
|   retval = 180./pi.*acos(x);

Why is the NaN assignment needed?  Doesn't

  retval = 180/pi*acos(x);

do the right thing?

| function retval = acotd (x)
| 
|   if (nargin != 1)
|     usage("acotd (x)");
|   end
| 
|   nz_x = find(x != 0);
|   retval = ones(size(x)).*90;
|   retval(nz_x) = 180./pi.*atan(1./x(nz_x));

Instead of these three lines, why not just use

  retval = 180/pi*acot(x);

?

Also, if we do decide that the checks are necessary, it is usually
better to write things like

  x(x != 0) = NaN;

instead of

  x(find (x != 0)) = NaN;

and if you are checking for infinity, please use isinf (x) instead of
x == inf.

Thanks,

jwe



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