From octave-sources-request at bevo dot che dot wisc dot edu  Fri Jul 14 21:28:19 2000
Subject: Re: matlab-like functions
From: pkienzle at kienzle dot powernet dot co dot uk (Paul Kienzle)
To: tpikonen at pcu dot helsinki dot fi
Cc: octave-sources at bevo dot che dot wisc dot edu
Date: Fri, 14 Jul 2000 17:19:47 +0100 (BST)

From: Teemu Ikonen <tpikonen at pcu dot helsinki dot fi>
>Hi,
>
>I downloaded yor matcompat collection today, good work!
>
>Checking out my own matlab-compatibility functions, I found that I have a
>slightly better mod function which handles the case mod(x,0) like matlab,
>ie. returns x, not NaN. I attached the file to this mail.

Slightly worse I would say.  Mod(x,0) is NaN even if matlab says
otherwise.  Okay, lim_{y->0+} mod(x,y) = 0, but that is still not what
matlab is returning.  The question is, do we really want to take a 50-80%
hit in execution time to support a documented non-feature, even if the
non-feature is not used?  If any(y==0), mod can be up to a 600% slower.

Note that your function do not support one argument being a scalar and the
other being a vector.  The following code fixes this, as well as being
somewhat faster.

Paul Kienzle
pkienzle at kienzle dot powernet dot co dot uk

function r=mod(x,y)

  if nargin != 2,
    usage("r=mod(x,y)");
  endif

  pzoi = prefer_zero_one_indexing;
  unwind_protect
    prefer_zero_one_indexing = 1;
    nz = y != 0.0;
    if all(all(nz))
      r = x - floor(x./y).*y;
    elseif is_scalar(y)
      r = x;
    elseif is_scalar(x)
      r = x*ones(size(y));
      y = y(nz);
      r(nz) = x - floor(x./y).*y;
    else
      r = x;
      x = x(nz);
      y = y(nz);
      r(nz) = x - floor(x./y).*y;
    endif
  unwind_protect_cleanup
    prefer_zero_one_indexing = pzoi;
  end_unwind_protect
endfunction



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