Hi, I've a matrix in 20*11 order. There are 11 variables, i.e 11 columns and each variable have 20 row data. Now i want to calculate covariance between any variable with others taking 4 rows at a time, so that there will be 5 blocks. How can i do this using any R-function? If i want to do it in any 'loop' function? Thanks a lot, SB.