lower.tri                package:base                R Documentation

Lower and Upper Triangular Part of a Matrix

Description:

     Returns a matrix of logicals the same size of a given matrix with
     entries `TRUE' in the lower or upper triangle.

Usage:

     lower.tri(x, diag = FALSE)
     upper.tri(x, diag = FALSE)

Arguments:

       x: a matrix.

    diag: logical. Should the diagonal be included?

See Also:

     `diag', `matrix'.

Examples:

     m2 <- ma <- matrix(1:20, 4, 5)
     m2[lower.tri(m2)] <- NA
     m2
     stopifnot(lower.tri(ma) == !upper.tri(ma, diag=TRUE))

