a=matrix(1:9,3,3)
b=matrix(0,3,3)
replaceBand(a,b,0)
#> [,1] [,2] [,3]
#> [1,] 0 4 7
#> [2,] 2 0 8
#> [3,] 3 6 0
replaceBand(a,b,1)
#> [,1] [,2] [,3]
#> [1,] 0 0 7
#> [2,] 0 0 0
#> [3,] 3 0 0
replaceBand(a,b,2)
#> [,1] [,2] [,3]
#> [1,] 0 0 0
#> [2,] 0 0 0
#> [3,] 0 0 0