Dropping columns and rows of huge matrix

Question

I have a huge matrix and would like to drop every other 4th row and every other 4th column in one shot. What is the element way to do that.

Regards,

Answer 1

Use Drop:

Drop[Array[a, {9, 9}], {4, -1, 4}, {4, -1, 4}] //TeXForm

$\left( \begin{array}{ccccccc} a(1,1) & a(1,2) & a(1,3) & a(1,5) & a(1,6) & a(1,7) & a(1,9) \\ a(2,1) & a(2,2) & a(2,3) & a(2,5) & a(2,6) & a(2,7) & a(2,9) \\ a(3,1) & a(3,2) & a(3,3) & a(3,5) & a(3,6) & a(3,7) & a(3,9) \\ a(5,1) & a(5,2) & a(5,3) & a(5,5) & a(5,6) & a(5,7) & a(5,9) \\ a(6,1) & a(6,2) & a(6,3) & a(6,5) & a(6,6) & a(6,7) & a(6,9) \\ a(7,1) & a(7,2) & a(7,3) & a(7,5) & a(7,6) & a(7,7) & a(7,9) \\ a(9,1) & a(9,2) & a(9,3) & a(9,5) & a(9,6) & a(9,7) & a(9,9) \\ \end{array} \right)$