Nothing
u.vectors <- function( n )
{
###
### This function constructs an identity matrix I of order
### p = n * ( n +1 ) / 2. It also builds a lower triangular square matrix of
### order n. The value of element [i,j] is the column number
### in the identify matrix. It is the mapping from the coordinates
### to the column vector in the identity matrix.
###
### argument
### n = a positive integer value
###
if ( n != trunc( n ) )
stop( "argument n is not an integer" )
if ( n < 2 )
stop( "argument n is less than 2" )
p <- n * ( n + 1 ) / 2
I <- diag( rep( 1, p ) )
k <- matrix( 0, nrow=n, ncol=n )
for ( j in 1:n ) {
for ( i in j:n ) {
k[i,j] <- ( j - 1 ) * n + i - 0.5 * j * ( j - 1 )
}
}
return( list( k=k, I=I ) )
}
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