1 ## Copyright (C) 2010-2012 John W. Eaton
3 ## This file is part of Octave.
5 ## Octave is free software; you can redistribute it and/or modify it
6 ## under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation; either version 3 of the License, or (at
8 ## your option) any later version.
10 ## Octave is distributed in the hope that it will be useful, but
11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 ## General Public License for more details.
15 ## You should have received a copy of the GNU General Public License
16 ## along with Octave; see the file COPYING. If not, see
17 ## <http://www.gnu.org/licenses/>.
20 ## @deftypefn {Function File} {} chop (@var{x}, @var{ndigits}, @var{base})
21 ## Truncate elements of @var{x} to a length of @var{ndigits} such that the
22 ## resulting numbers are exactly divisible by @var{base}. If @var{base} is not
23 ## specified it defaults to 10.
28 ## @result{} -3.14200000000000
30 ## @result{} -3.14150000000000
35 function retval = chop (x, ndigits, base = 10)
37 if (nargin == 2 || nargin == 3)
40 ## Avoid computing log (0).
43 ## Digits to the left of the decimal.
44 tmp = floor (log10 (tmp) + 1);
48 ## round (x .* inflate)
50 ## produces an integer that contains the digits we want to keep.
51 ## Multiplying by deflate puts the decimal back where it belngs.
53 ## Further scaling and rounding with the base factor produces a
54 ## value with ndigits exactly divisible by base. We skip that step
55 ## unless base was explicitly provided.
57 inflate = 10 .^ (ndigits - tmp);
58 deflate = 10 .^ (tmp - ndigits);
60 retval = deflate .* round (x .* inflate);
62 retval = base .* deflate .* round (round (x .* inflate) ./ base);
71 %!assert (chop (e, 3), 2.72)
72 %!assert (chop (e, 4), 2.718)
73 %!assert (chop (e, 4, 5), 2.72)
74 %!assert (chop (e, 4, 7), 2.716)
75 %!assert (chop (-e, 3), -2.72)
76 %!assert (chop (-e, 4), -2.718)
77 %!assert (chop (-e, 4, 5), -2.72)
78 %!assert (chop (-e, 4, 7), -2.716)
79 %!assert (chop (hilb (3), 3), [1,.5,.333;.5,.333,.25;.333,.25,.2])
80 %!assert (chop (hilb (3), 2, 7), [.7,.49,.35;.49,.35,.28;.35,.28,.21], 2*eps)