How to remove certain rows and columns in a matrix?

I have this 8x8 matrix and I want to preserve only the 1, 2, 7 and 8 (for now, these numbers change based on a computation) rows and column to get a 4x4 output matrix. How can I delete other columns and rows or copy the forementioned rows and columns to a new matrix with a new 4x4 structure?

Keep in mind that the desired rows and columns change based on a function computation.

A = [

0 1 0 0 0 0 0 1

1 0 0 0 0 0 1 0

0 0 0 0 1 0 0 0

0 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0

0 0 0 1 0 0 0 0

0 1 0 0 0 0 0 1

1 0 0 0 0 0 1 0 ]

Desired output (for this context):

A = [

0 1 0 1

1 0 1 0

0 1 0 1

1 0 1 0 ]

[Stephen23]

>> B = A([1,2,7,8],[1,2,7,8])
B =
   0   1   0   1
   1   0   1   0
   0   1   0   1
   1   0   1   0

[Ali]

Thanks @Stephen, nice and clean solution. ;)

Answer 1

[madhan ravi]

 w = A([1,2,7,8], :)
 Wanted = w(:, [1,2,7,8])

[Ali]

You're a lifesaver buddy! Respect! :)