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1 ## Copyright (C) 1996, 1997 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 2, or (at your option) |
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8 ## 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, write to the Free |
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17 ## Software Foundation, 59 Temple Place - Suite 330, Boston, MA |
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18 ## 02111-1307, USA. |
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19 |
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20 ## usage: triu (x, k) |
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21 ## |
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22 ## Return the lower triangular part of x above the k-th diagonal. If |
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23 ## the second argument is omitted, k = 0 is assumed. |
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24 ## |
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25 ## See also: triu, diag |
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26 |
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27 ## Author: jwe |
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28 |
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29 function retval = tril (x, k) |
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30 |
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31 if (nargin > 0) |
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32 [nr, nc] = size (x); |
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33 retval = zeros (nr, nc); |
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34 endif |
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35 |
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36 if (nargin == 1) |
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37 k = 0; |
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38 elseif (nargin == 2) |
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39 if ((k > 0 && k > nc) || (k < 0 && k < -nr)) |
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40 error ("tril: requested diagonal out of range"); |
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41 endif |
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42 else |
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43 usage ("tril (x [, k])"); |
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44 endif |
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45 |
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46 for j = 1 : min (nc, nr+k) |
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47 nr_limit = max (1, j-k); |
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48 retval (nr_limit:nr, j) = x (nr_limit:nr, j); |
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49 endfor |
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50 |
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51 endfunction |
