The “Other” Diagonal Matrix

Compute the other diagonal identity matrix. The result is basically a fast version of diag(n)[, n:1].

Usage

diagX(n)

Arguments

n

positive integer.

Value

a numeric \(n \times n\) matrix with many zeros – apart from 1s in the other diagonal.

Author

Martin Maechler, 1992.

See also

diag.

Examples

diagX(4)
#>      [,1] [,2] [,3] [,4]
#> [1,]    0    0    0    1
#> [2,]    0    0    1    0
#> [3,]    0    1    0    0
#> [4,]    1    0    0    0
for(m in 1:5)
  stopifnot(identical(diagX(m), diag(m)[, m:1, drop = FALSE]))