How to create a semi-diagonal matrix

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Konstantinos Tsitsilonis 2017-11-21

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评论： Konstantinos Tsitsilonis 2017-11-22

Hi all,

I have been trying to create a semi-diagonal matrix; Now I know this may not be the right terminology for it, however here it is (also, the matrix doesnt have to be square. I want to have control over its m x n dimensions. The example is thus of a semi-diagonal 3 x 6 matrix):

 M_3x6 = [1 1 0 0 0 0
          0 0 1 1 0 0
          0 0 0 0 1 1] ;

Or for a larger matrix:

 M_4x7 = [1 1 0 0 0 0 0
          0 0 1 1 0 0 0
          0 0 0 0 1 1 0
          0 0 0 0 0 0 1] ;

Thanks for your help in advance,

KMT.

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Answer 1

Stephen23 2017-11-21

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编辑：Stephen23 2017-11-21

在 MATLAB Online 中打开

Method one: blkdiag:

>> blkdiag([1,1],[1,1],[1,1])
ans =
   1   1   0   0   0   0
   0   0   1   1   0   0
   0   0   0   0   1   1
>>

You can easily supply the inputs as a comma-separated list:

>> C = repmat({[1,1]},1,4);
>> blkdiag(C{:})
ans =
   1   1   0   0   0   0   0   0
   0   0   1   1   0   0   0   0
   0   0   0   0   1   1   0   0
   0   0   0   0   0   0   1   1
>>

Then use indexing to select a part of the matrix.

Method two: repelem: With newer MATLAB versions you could use eye and repelem, and then use indexing as above.