Last change
on this file since 177 was
37,
checked in by (none), 15 years ago
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Added original make3d
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Property svn:executable set to
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File size:
768 bytes
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1 | function h = vgg_vech(m)
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2 | % VGG_VECH Vectorization ("flattening") of symmetric matrix.
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3 | %
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4 | % For square matrix X, vgg_vech(X) is the column vector of elements on or
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5 | % below the main diagonal of m.
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6 | %
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7 | % Also works inversely: for a N*(N+1)/2-vector x, it returns symmetric
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8 | % N-by-N matrix X = vgg_vech(x) such that vgg_vech(X) = x.
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9 | %
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10 | % Useful for solving linear matrix equations, see Magnus and Neudecker.
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11 | %
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12 | % See vgg_matrix_test, vgg_duplic_matrix, and also vgg_vech_swap,
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13 | % vgg_commut_matrix.
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14 |
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15 | [M N] = size(m);
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16 |
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17 | if M==1 | N==1
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18 | N = (sqrt(8*M*N+1)-1)/2;
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19 | r = (1:N)'*ones(1,N);
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20 | c = r';
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21 | h = zeros(N);
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22 | h(find(c <= r)) = m;
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23 | h = h+h'-diag(diag(h));
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24 | else
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25 | r = (1:M)'*ones(1,N);
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26 | c = ones(M,1)*(1:N);
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27 | h = m(find(c <= r));
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28 | end
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29 |
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30 | return |
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