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1 ## Copyright (C) 2003 David Bateman |
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2 ## |
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3 ## This program is free software; you can redistribute it and/or modify it under |
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4 ## the terms of the GNU General Public License as published by the Free Software |
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5 ## Foundation; either version 3 of the License, or (at your option) any later |
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6 ## version. |
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7 ## |
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8 ## This program is distributed in the hope that it will be useful, but WITHOUT |
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9 ## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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10 ## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more |
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11 ## details. |
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12 ## |
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13 ## You should have received a copy of the GNU General Public License along with |
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14 ## this program; if not, see <http://www.gnu.org/licenses/>. |
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15 |
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16 ## -*- texinfo -*- |
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17 ## @deftypefn {Function File} {} convmtx (@var{a}, @var{n}) |
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18 ## |
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19 ## Create matrix to perform repeated convolutions with the same vector |
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20 ## in a Galois Field. If @var{a} is a column vector and @var{x} is a |
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21 ## column vector of length @var{n}, in a Galois Field then |
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22 ## |
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23 ## @code{convmtx(@var{a}, @var{n}) * @var{x}} |
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24 ## |
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25 ## gives the convolution of of @var{a} and @var{x} and is the |
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26 ## same as @code{conv(@var{a}, @var{x})}. The difference is if |
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27 ## many vectors are to be convolved with the same vector, then |
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28 ## this technique is possibly faster. |
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29 ## |
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30 ## Similarly, if @var{a} is a row vector and @var{x} is a row |
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31 ## vector of length @var{n}, then |
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32 ## |
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33 ## @code{@var{x} * convmtx(@var{a}, @var{n})} |
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34 ## |
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35 ## is the same as @code{conv(@var{x}, @var{a})}. |
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36 ## @end deftypefn |
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37 ## @seealso{conv} |
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38 |
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39 function b = convmtx (a, n) |
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40 |
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41 if (!isgalois (a)) |
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42 error("convmtx: argument must be a galois variable"); |
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43 endif |
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44 |
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45 b = gf(convmtx(a.x,n), a.m, a.prim_poly); |
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46 |
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47 endfunction |
