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1 ## Copyright (C) 2004 David Bateman & Andy Adler |
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2 ## |
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3 ## This program is free software; you can redistribute it and/or modify |
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4 ## it under the terms of the GNU General Public License as published by |
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5 ## the Free Software Foundation; either version 2 of the License, or |
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6 ## (at your option) any later version. |
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7 ## |
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8 ## This program is distributed in the hope that it will be useful, |
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9 ## but WITHOUT ANY WARRANTY; without even the implied warranty of |
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10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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11 ## GNU General Public License for more details. |
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12 ## |
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13 ## You should have received a copy of the GNU General Public License |
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14 ## along with this program; if not, write to the Free Software |
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15 ## Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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16 ## 02110-1301 USA |
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17 |
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18 ## -*- texinfo -*- |
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19 ## @deftypefn {Function File} {@var{y} =} speye (@var{m}) |
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20 ## @deftypefnx {Function File} {@var{y} =} speye (@var{m}, @var{n}) |
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21 ## @deftypefnx {Function File} {@var{y} =} speye (@var{sz}) |
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22 ## Returns a sparse identity matrix. This is significantly more |
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23 ## efficient than @code{sparse (eye (@var{m}))} as the full matrix |
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24 ## is not constructed. |
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25 ## |
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26 ## Called with a single argument a square matrix of size @var{m} by |
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27 ## @var{m} is created. Otherwise a matrix of @var{m} by @var{n} is |
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28 ## created. If called with a single vector argument, this argument |
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29 ## is taken to be the size of the matrix to create. |
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30 ## @end deftypefn |
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31 |
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32 function s = speye (m, n) |
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33 if (nargin == 1) |
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34 if (isvector (m) && length(m) == 2) |
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35 n = m(2); |
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36 m = m(1); |
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37 elseif (isscalar (m)) |
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38 n = m; |
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39 else |
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40 error ("speye: invalid matrix dimension"); |
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41 endif |
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42 else |
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43 if (! isscalar (m) || ! isscalar (n)) |
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44 error ("speye: invalid matrix dimension"); |
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45 endif |
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46 endif |
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47 |
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48 lo = min ([m, n]); |
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49 s = sparse (1:lo, 1:lo, 1, m, n); |
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50 endfunction |
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51 |
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52 %!assert(issparse(speye(4))) |
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53 %!assert(speye(4),sparse(1:4,1:4,1)) |
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54 %!assert(speye(2,4),sparse(1:2,1:2,1,2,4)) |
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55 %!assert(speye(4,2),sparse(1:2,1:2,1,4,2)) |
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56 %!assert(speye([4,2]),sparse(1:2,1:2,1,4,2)) |
