update packages

[CreaPhase.git] / octave_packages / m / general / chop.m

diff --git a/octave_packages/m/general/chop.m b/octave_packages/m/general/chop.m
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+## Copyright (C) 2010-2012 John W. Eaton
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} chop (@var{x}, @var{ndigits}, @var{base})
+## Truncate elements of @var{x} to a length of @var{ndigits} such that the
+## resulting numbers are exactly divisible by @var{base}.  If @var{base} is not
+## specified it defaults to 10.
+##
+## @example
+## @group
+## chop (-pi, 5, 10)
+##    @result{} -3.14200000000000
+## chop (-pi, 5, 5)
+##    @result{} -3.14150000000000
+## @end group
+## @end example
+## @end deftypefn
+
+function retval = chop (x, ndigits, base = 10)
+
+  if (nargin == 2 || nargin == 3)
+    tmp = abs (x);
+
+    ## Avoid computing log (0).
+    tmp(x == 0) = 1;
+
+    ## Digits to the left of the decimal.
+    tmp = floor (log10 (tmp) + 1);
+
+    ## The expression
+    ##
+    ##   round (x .* inflate)
+    ##
+    ## produces an integer that contains the digits we want to keep.
+    ## Multiplying by deflate puts the decimal back where it belngs.
+    ##
+    ## Further scaling and rounding with the base factor produces a
+    ## value with ndigits exactly divisible by base.  We skip that step
+    ## unless base was explicitly provided.
+
+    inflate = 10 .^ (ndigits - tmp);
+    deflate = 10 .^ (tmp - ndigits);
+    if (nargin == 2)
+      retval = deflate .* round (x .* inflate);
+    else
+      retval = base .* deflate .* round (round (x .* inflate) ./ base);
+    endif
+  else
+    print_usage ();
+  endif
+
+endfunction
+
+
+%!assert (chop (e, 3), 2.72)
+%!assert (chop (e, 4), 2.718)
+%!assert (chop (e, 4, 5), 2.72)
+%!assert (chop (e, 4, 7), 2.716)
+%!assert (chop (-e, 3), -2.72)
+%!assert (chop (-e, 4), -2.718)
+%!assert (chop (-e, 4, 5), -2.72)
+%!assert (chop (-e, 4, 7), -2.716)
+%!assert (chop (hilb (3), 3), [1,.5,.333;.5,.333,.25;.333,.25,.2])
+%!assert (chop (hilb (3), 2, 7), [.7,.49,.35;.49,.35,.28;.35,.28,.21], 2*eps)