Mercurial > matrix-functions
comparison mftoolbox/power_binary.m @ 0:8f23314345f4 draft
Create local repository for matrix toolboxes. Step #0 done.
| author | Antonio Pino Robles <data.script93@gmail.com> |
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| date | Wed, 06 May 2015 14:56:53 +0200 |
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| -1:000000000000 | 0:8f23314345f4 |
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| 1 function X = power_binary(A,m) | |
| 2 %POWER_BINARY Power of matrix by binary powering (repeated squaring). | |
| 3 % X = POWER_BINARY(A,m) computes A^m for a square matrix A and a | |
| 4 % positive integer m, by binary powering. | |
| 5 | |
| 6 s = double(dec2bin(m)) - 48; % Binary representation of s in double array. | |
| 7 k = length(s); | |
| 8 | |
| 9 P = A; | |
| 10 i = k; | |
| 11 while s(i) == 0 | |
| 12 P = P^2; | |
| 13 i = i-1; | |
| 14 end | |
| 15 X = P; | |
| 16 for j = i-1:-1:1 | |
| 17 P = P^2; | |
| 18 if s(j) == 1 | |
| 19 X = X*P; | |
| 20 end | |
| 21 | |
| 22 end |