Lower and Upper Triangular Part of a Sparse Matrix

Returns the lower or upper triangular structure or entries of a sparse matrix.

Usage

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

Arguments

x

a sparse matrix of class spam

diag

logical. Should the diagonal be included?

Details

Often not only the structure of the matrix is required but the entries as well. For compatibility, the default is only a structure consisting of ones (representing TRUEs). Setting the flag getOption( "spam.trivalues") to TRUE, the function returns the actual values.

See also

spam.options and diag

Examples

smat <- spam( c( 1,2,0,3,0,0,0,4,5),3)
upper.tri( smat)
#>      [,1] [,2] [,3]
#> [1,]    0    1    0
#> [2,]    0    0    1
#> [3,]    0    0    0
#> Class 'spam' (32-bit)
upper.tri( smat, diag=TRUE)
#>      [,1] [,2] [,3]
#> [1,]    1    1    0
#> [2,]    0    0    1
#> [3,]    0    0    1
#> Class 'spam' (32-bit)

options(spam.trivalues=TRUE)
upper.tri( smat)
#>      [,1] [,2] [,3]
#> [1,]    0    3    0
#> [2,]    0    0    4
#> [3,]    0    0    0
#> Class 'spam' (32-bit)