MATLAB: To split a matrix into equal parts.

matrix manipulation

Hi, Thanks to your answers, but did not get it properly. I am making it simpler by considering for a 6 by 6 matrix.Suppose I have a 6 by 6 matrix where the elements vary from 1:36 in increment of 1. When I split it into 4 equal matrix the matrices should be:a(say)=[1 2 3; 7 8 9; 13 14 15],b(say)=[4 5 6;10 11 12; 16 17 18],c=[19 20 21;25 26 27; 31 32 33],d=[22 23 24;28 29 30; 34 35 36].Now, when I choose the middle element to construct a new matrix it should be M(say)=[8 11; 26 29]. Now, my question lies simply to generalize it for a 128 by 128 matrix. Thankin you!

Best Answer

Hi,

still the same answer as before:

a = reshape(1:36,6,6)
 b = a(2:3:end,2:3:end)'

So when usingg 128x128 matrix:

a = reshape(1:128*128,128,128);
b = a(16:32:end,16:32:end)'

Related Solutions

MATLAB: How to plot a matrix on a 3D graph

[xx yy] = meshgrid(M(1,2:end),M(2:end,1));
plot3(xx(:),yy(:),reshape(M(2:end,2:end),[],1));

or surf or mesh whatever type of plot you want.

Addendum The best way to learn is to do it yourself and break down every line to see what's happening.

%Sample script to identify every op.
M = magic(6)
[xx yy] = meshgrid(M(1,2:end),M(2:end,1))
disp('M(2:end,2:end) = ');
M(2:end,2:end)
disp('M reshaped to column vector: ')
reshape(M(2:end,2:end),[],1)

M =

    35     1     6    26    19    24
     3    32     7    21    23    25
    31     9     2    22    27    20
     8    28    33    17    10    15
    30     5    34    12    14    16
     4    36    29    13    18    11

xx =

     1     6    26    19    24
     1     6    26    19    24
     1     6    26    19    24
     1     6    26    19    24
     1     6    26    19    24

yy =

     3     3     3     3     3
    31    31    31    31    31
     8     8     8     8     8
    30    30    30    30    30
     4     4     4     4     4

M(2:end,2:end) =

ans =

    32     7    21    23    25
     9     2    22    27    20
    28    33    17    10    15
     5    34    12    14    16
    36    29    13    18    11

M reshaped to column vector:

ans =

The xx(:) operation does the same thing as reshape in this use of reshape.

MATLAB: How to reshape a matrix into nx2 matrix

reshape( A( :, [ 1:2:end, 2:2:end ] ), [], 2 )

You may wish to change the final two arguments to the reshape command in different situations.

doc reshape

tells you about these.

You can be explicit and pass in the exact size as [18, 2] or 18, 2 if you wish or you could pass in 18, []

In this case all would give the same answer. The [] input is allowed for one dimension and just tells it to work out that value in order to use all elements. Obviously the product of all the dimensions you resize to must be equal to the number of elements in the array being resized.

Best Answer

Related Solutions

MATLAB: How to plot a matrix on a 3D graph

MATLAB: How to reshape a matrix into nx2 matrix

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