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1 # Copyright (C) 1993, 1994, 1995 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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19 function retval = hankel (c, r) |
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20 |
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21 # usage: hankel (c, r) |
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22 # |
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23 # Return the Hankel matrix constructed given the first column |
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24 # c, and (optionally) the last row r. |
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25 # |
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26 # If the second argument is omitted, zeros are inserted below the main |
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27 # anti-diagonal. If the last element of c is not the same as the first |
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28 # element of r, the last element of c is used. |
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29 # |
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30 # See also: vander, hadamard, hilb, invhilb, toeplitz |
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31 |
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32 if (nargin == 1) |
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33 r = zeros (size (c)); |
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34 elseif (nargin != 2) |
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35 usage ("hankel (c, r)"); |
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36 endif |
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37 |
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38 [c_nr, c_nc] = size (c); |
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39 [r_nr, r_nc] = size (r); |
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40 |
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41 if ((c_nr != 1 && c_nc != 1) || (r_nr != 1 && r_nc != 1)) |
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42 error ("hankel: expecting vector arguments"); |
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43 endif |
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44 |
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45 if (nargin == 1) |
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46 r (1) = c (length (c)); |
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47 endif |
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48 |
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49 if (c_nc != 1) |
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50 c = c.'; |
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51 endif |
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52 |
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53 if (r_nr != 1) |
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54 r = r.'; |
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55 endif |
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56 |
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57 nc = length (r); |
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58 nr = length (c); |
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59 |
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60 if (r (1) != c (nr)) |
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61 warning ("hankel: column wins anti-diagonal conflict"); |
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62 endif |
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63 |
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64 # This should probably be done with the colon operator... |
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65 |
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66 retval = zeros (nr, nc); |
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67 |
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68 for i = 1:min (nr, nc) |
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69 retval (1:nr-i+1, i) = c (i:nr); |
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70 endfor |
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71 |
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72 tmp = 1; |
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73 if (nc <= nr) |
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74 tmp = nr - nc + 2; |
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75 endif |
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76 |
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77 for i = nr:-1:tmp |
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78 retval (i, 2+nr-i:nc) = r (2:nc-nr+i); |
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79 endfor |
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80 |
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81 endfunction |
