|
2847
|
1 ## Copyright (C) 1996, 1997 John W. Eaton |
|
2313
|
2 ## |
|
|
3 ## This file is part of Octave. |
|
|
4 ## |
|
|
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 |
|
7016
|
7 ## the Free Software Foundation; either version 3 of the License, or (at |
|
|
8 ## your option) any later version. |
|
2313
|
9 ## |
|
|
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. |
|
|
14 ## |
|
|
15 ## You should have received a copy of the GNU General Public License |
|
7016
|
16 ## along with Octave; see the file COPYING. If not, see |
|
|
17 ## <http://www.gnu.org/licenses/>. |
|
245
|
18 |
|
3369
|
19 ## -*- texinfo -*- |
|
|
20 ## @deftypefn {Function File} {} tril (@var{a}, @var{k}) |
|
|
21 ## @deftypefnx {Function File} {} triu (@var{a}, @var{k}) |
|
5668
|
22 ## Return a new matrix formed by extracting the lower (@code{tril}) |
|
3369
|
23 ## or upper (@code{triu}) triangular part of the matrix @var{a}, and |
|
|
24 ## setting all other elements to zero. The second argument is optional, |
|
|
25 ## and specifies how many diagonals above or below the main diagonal should |
|
|
26 ## also be set to zero. |
|
3426
|
27 ## |
|
3369
|
28 ## The default value of @var{k} is zero, so that @code{triu} and |
|
|
29 ## @code{tril} normally include the main diagonal as part of the result |
|
|
30 ## matrix. |
|
3426
|
31 ## |
|
3369
|
32 ## If the value of @var{k} is negative, additional elements above (for |
|
|
33 ## @code{tril}) or below (for @code{triu}) the main diagonal are also |
|
|
34 ## selected. |
|
3426
|
35 ## |
|
3369
|
36 ## The absolute value of @var{k} must not be greater than the number of |
|
|
37 ## sub- or super-diagonals. |
|
3426
|
38 ## |
|
3369
|
39 ## For example, |
|
3426
|
40 ## |
|
3369
|
41 ## @example |
|
|
42 ## @group |
|
|
43 ## tril (ones (3), -1) |
|
|
44 ## @result{} 0 0 0 |
|
|
45 ## 1 0 0 |
|
|
46 ## 1 1 0 |
|
|
47 ## @end group |
|
|
48 ## @end example |
|
3426
|
49 ## |
|
3369
|
50 ## @noindent |
|
|
51 ## and |
|
3426
|
52 ## |
|
3369
|
53 ## @example |
|
|
54 ## @group |
|
|
55 ## tril (ones (3), 1) |
|
|
56 ## @result{} 1 1 0 |
|
|
57 ## 1 1 1 |
|
|
58 ## 1 1 1 |
|
|
59 ## @end group |
|
|
60 ## @end example |
|
5642
|
61 ## @seealso{triu, diag} |
|
3369
|
62 ## @end deftypefn |
|
4
|
63 |
|
2314
|
64 ## Author: jwe |
|
|
65 |
|
2311
|
66 function retval = tril (x, k) |
|
4
|
67 |
|
|
68 if (nargin > 0) |
|
|
69 [nr, nc] = size (x); |
|
5731
|
70 retval = resize (resize (x, 0), nr, nc); |
|
4
|
71 endif |
|
|
72 |
|
|
73 if (nargin == 1) |
|
|
74 k = 0; |
|
|
75 elseif (nargin == 2) |
|
1083
|
76 if ((k > 0 && k > nc) || (k < 0 && k < -nr)) |
|
1518
|
77 error ("tril: requested diagonal out of range"); |
|
4
|
78 endif |
|
|
79 else |
|
6046
|
80 print_usage (); |
|
4
|
81 endif |
|
|
82 |
|
2015
|
83 for j = 1 : min (nc, nr+k) |
|
1083
|
84 nr_limit = max (1, j-k); |
|
|
85 retval (nr_limit:nr, j) = x (nr_limit:nr, j); |
|
4
|
86 endfor |
|
|
87 |
|
|
88 endfunction |
