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changing arrays of a matrix

Asked by ss on 27 Dec 2012

Hi

if we have a matrix and we want to change the position of its array, rows and columns simultaneously, using two index vector B1 and B2, how can we use this command, i.e for instance u=[u11 u12 u13 u14;u21 u22 u23 u24;u31 u32 u33 u34;u41 u42 u43 u44]; B1=[1 4 3 2] B2=[3 2 1 4](B1 and B2 themselves are columns of a matrix) such that B1 is used for changing rows and B2 for changing columns, so u would be u=[u13 u12 u11 u14;u43 u42 u41 u44;u33 u32 u31 u34; u23 u22 u21 u24] thanks

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ss

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2 Answers

Answer by Jan Simon on 27 Dec 2012
Edited by Jan Simon on 27 Dec 2012
Accepted answer

You can simply use the index vectors to resort rows and columns:

u = [11    12    13    14; ...
     21    22    23    24; ...
     31    32    33    34; ...
     41    42    43    44];
B1 = [1 4 3 2];
B2 = [3 2 1 4];
u = u(B1, B2);
>> u = 
  13    12    11    14
  43    42    41    44
  33    32    31    34
  23    22    21    24

1 Comment

ss on 29 Dec 2012

and what should we do if size of matrix is bigger than B1 and B2, for instance (u)6*6 and B1 and B2 are 4*4? thanks

Jan Simon
Answer by Azzi Abdelmalek on 27 Dec 2012
Edited by Azzi Abdelmalek on 27 Dec 2012
u=magic(4)     % Example of u
n=size(u,1)
B1=randperm(n)  % Example of B1
B2=randperm(n)' % Example of B2
u=u(:,B1)       
u=u(B2,:)

1 Comment

Jan Simon on 27 Dec 2012

You can omit the transposition for B2.

Azzi Abdelmalek

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