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annotate toolbox/sparsify.m @ 0:8f23314345f4 draft

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Create local repository for matrix toolboxes. Step #0 done.
author Antonio Pino Robles <data.script93@gmail.com>
date Wed, 06 May 2015 14:56:53 +0200
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8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
Antonio Pino Robles <data.script93@gmail.com>
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1 function A = sparsify(A, p)
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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2 %SPARSIFY Randomly sets matrix elements to zero.
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3 % S = SPARSIFY(A, P) is A with elements randomly set to zero
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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4 % (S = S' if A is square and A = A', i.e. symmetry is preserved).
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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5 % Each element has probability P of being zeroed.
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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6 % Thus on average 100*P percent of the elements of A will be zeroed.
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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7 % Default: P = 0.25.
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8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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9 if nargin < 2, p = 0.25; end
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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10 if p<0 | p>1, error('Second parameter must be between 0 and 1 inclusive.'), end
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11
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12 % Is A square and symmetric?
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13 symm = 0;
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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14 if min(size(A)) == max(size(A))
8f23314345f4 Create local repository for matrix toolboxes. Step #0 done.
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15 if norm(A-A',1) == 0, symm = 1; end
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16 end
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17
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18 if ~symm
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19 A = A .* (rand(size(A)) > p); % Unsymmetric case
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20 else
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21 A = triu(A,1) .* (rand(size(A)) > p); % Preserve symmetry
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22 A = A + A';
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23 A = A + diag( diag(A) .* (rand(size(diag(A))) > p) );
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24 end