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1 # Copyright (C) 1996 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 the |
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7 # Free Software Foundation; either version 2, or (at your option) any |
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8 # later version. |
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9 # |
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10 # Octave is distributed in the hope that it will be useful, but WITHOUT |
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11 # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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12 # FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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13 # 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, write to the Free |
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17 # Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
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18 |
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4
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19 function retval = tril (x, k) |
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20 |
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21 # usage: triu (x, k) |
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22 # |
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23 # Return the lower triangular part of x above the k-th diagonal. If |
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24 # the second argument is omitted, k = 0 is assumed. |
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25 # |
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26 # See also: triu, diag |
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27 |
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28 if (nargin > 0) |
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29 [nr, nc] = size (x); |
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30 retval = zeros (nr, nc); |
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4
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31 endif |
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32 |
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33 if (nargin == 1) |
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34 k = 0; |
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35 elseif (nargin == 2) |
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36 if ((k > 0 && k > nc) || (k < 0 && k < -nr)) |
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37 error ("tril: requested diagonal out of range"); |
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4
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38 endif |
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39 else |
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40 usage ("tril (x [, k])"); |
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4
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41 endif |
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42 |
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43 for j = 1 : min (nc, nc + abs (k)) |
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44 nr_limit = max (1, j-k); |
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45 retval (nr_limit:nr, j) = x (nr_limit:nr, j); |
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4
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46 endfor |
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47 |
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48 endfunction |
