Central part of a matrix

Hello,

If a have a Matrix M and I want to create a new one, call it Central_M, which should be the central part of M and of a defined size s, how can I do it?

 M_central = ?

Thanks in advance for your reply.

[Chris McComb]

What exactly do you mean by 'central'? And can you define s?

[Auryn_]

Central means that I want to take only the central part of the matrix of a defined size s. s = imcrop(I,[max(1,i-10) max(1,j-10) 23 23]);

Answer 1

[Jos (10584)]

Something like this?

M = spiral(10) % test matrix
S = 2  % s elements around the central position
% the resulting matrix will be 2*S+1 squared in size

dx = -S:S ;

RC0 = ceil(size(M)/2) % central position
OUT = M(RC0(1)+dx, RC0(2)+dx)

[Sean de Wolski]

+1 for spiral!

Answer 2

[RAGHAVENDRA]

M_central=M(floor(size(M,1)/2)-floor(s/2):floor(size(M,1)/2)+floor(s/2),floor(size(M,2)/2)-floor(s/2):floor(size(M,2)/2)+floor(s/2));

The above instruction will work, you can use 'round' instead of 'floor' to change the matrix indices accordingly.

[Guillaume]

Please use the {} Code button to format code in your answer

[Auryn_]

I receive an error message :(

[RAGHAVENDRA]

It is working perfectly for me, this is the example that i have tried

M=randi(5,[10 10]);

s=2;

M_central=M(floor(size(M,1)/2)-floor(s/2):floor(size(M,1)/2)+floor(s/2),floor(size(M,2)/2)-floor(s/2):floor(size(M,2)/2)+floor(s/2))

What is the error message?