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1 ## Copyright (C) 2010 John W. Eaton |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by |
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7 ## the Free Software Foundation; either version 3 of the License, or (at |
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8 ## your option) any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, see |
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17 ## <http://www.gnu.org/licenses/>. |
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18 |
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19 ## -*- texinfo -*- |
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20 ## @deftypefn {Function File} chop (@var{x}, @var{d}, @var{u}) |
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21 ## Truncate elements of @var{x} to @var{d} digits such that the |
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22 ## resulting digits are exactly divisible by @var{u}. If @var{u} is not |
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23 ## specified it defaults to 10. |
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24 ## |
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25 ## @example |
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26 ## @group |
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27 ## chop (-pi, 5, 10) |
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28 ## @result{} -3.14200000000000 |
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29 ## chop (-pi, 5, 5) |
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30 ## @result{} -3.14150000000000 |
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31 ## @end group |
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32 ## @end example |
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33 ## @end deftypefn |
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34 |
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35 function retval = chop (x, digits, units = 10) |
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36 |
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37 if (nargin == 2 || nargin == 3) |
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38 tmp = abs (x); |
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39 |
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40 ## Avoid computing log (0). |
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41 tmp(x == 0) = 1; |
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42 |
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43 ## Digits to the left of the decimal. |
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44 tmp = floor (log10 (tmp) + 1); |
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45 |
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46 ## The expression |
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47 ## |
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48 ## round (x .* inflate) |
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49 ## |
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50 ## produces an integer that contains the digits we want to keep. |
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51 ## Multiplying by deflate puts the decimal back where it belngs. |
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52 ## |
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53 ## Further scaling and rounding with the units factor produces a |
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54 ## value with digits exactly divisible by units. We skip that step |
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55 ## unless units was explicitly provided. |
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56 |
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57 inflate = 10 .^ (digits - tmp); |
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58 deflate = 10 .^ (tmp - digits); |
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59 if (nargin == 2) |
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60 retval = deflate .* round (x .* inflate); |
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61 else |
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62 retval = units .* deflate .* round (round (x .* inflate) ./ units); |
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63 endif |
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64 else |
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65 print_usage (); |
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66 endif |
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67 |
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68 endfunction |
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69 |
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70 %!assert (chop (e, 3), 2.72) |
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71 %!assert (chop (e, 4), 2.718) |
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72 %!assert (chop (e, 4, 5), 2.72) |
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73 %!assert (chop (e, 4, 7), 2.716) |
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74 %!assert (chop (-e, 3), -2.72) |
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75 %!assert (chop (-e, 4), -2.718) |
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76 %!assert (chop (-e, 4, 5), -2.72) |
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77 %!assert (chop (-e, 4, 7), -2.716) |
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78 %!assert (chop (hilb (3), 3), [1,.5,.333;.5,.333,.25;.333,.25,.2]) |
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79 %!assert (chop (hilb (3), 2, 7), [.7,.49,.35;.49,.35,.28;.35,.28,.21], 2*eps) |
