Cut around the center of a matrix

Hi everyone,

I have a quick question which may be simple to answer. I have a matrix,

A = [ 5 5 5 5 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 5 5 5 5 ]

'A' is always an odd number of lines and columns, and may be 100s of them. I want to cut at my own convenience a portion around the center, like

B = [ 4 4 4 ; 4 4 4 ; 4 4 4 ]

How can I do it?

Thanks

Answer 1

[Image Analyst]

Try this:

margin = 1; % Whatever you want.
B = A(margin+1:margin+1, end-margin:end-margin);

[maubars]

Results

B=4

[Image Analyst]

Thanks. Fix:

A = [ 5 5 5 5 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 5 5 5 5 ]
margin = 1; % Whatever you want.
B = A(margin + 1 : (end - margin), margin + 1 : (end - margin))

A =

5 5 5 5 5

5 4 4 4 5

5 4 4 4 5

5 4 4 4 5

5 5 5 5 5

B =

4 4 4

4 4 4

4 4 4

Answer 2

[Thorsten]

 szcut = 3;
 i1 = (size(A, 1) - szcut)/2;
 ind1 = i1+1:i1+szcut;
 B = A(ind1, ind2);

If A is not square or if you want to cut out non-square parts, define ind2 analogously.

Answer 3

[Michael Haderlein]

If c indicates the range you want to remove and would be 3 in your example, just use

 B=A((end-c)/2+1:(end+c)/2,(end-c)/2+1:(end+c)/2);

[I.G]

Can you make it for an arbitrary number of lines and rows? Like cx, cy

For example, say 'A is a 7x5 matrix full of '4s' inside.

[Thorsten]

Please see my answer above.

[Image Analyst]

In general it's B = A(row1:row2, column1:column2). You can decide on the rows and columns in any way that you want. If you want to get only a particular value (like 4) automatically (even if it's not a rectangle) then let me know. It's possible.

[I.G]

I made it like this:

cx=ceil(size(A,1)/2); % cx is the center line cy=ceil(size(A,2)/2); % cy is the center row x= ... % the steps in x axis from center x y= ... % the steps in y axis from center y B=A((cx-y):(cx+y),(cy-x):(cy+x));

Thanks for the help!