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Efficent way to create an nxn upper triangular matrix of one's

David Winsemius 
The other solutions offered are perfectly workable. Here is a strategy  
that is generalizable to other matrix designs (and on checking the  
source of upper.tri and lower.tri, it's not surprising that they use  
precisely the same strategy):

n <- 9
dm <- matrix(0, nrow=n, ncol=n)

dm[col(dm) >= row(dm)] <- 1

If you wanted only upper off-diagonal -1's, for instance, you could  
use instead:

dm[col(dm) == (row(dm)+1) ] <- -1

Thread (5 messages)

Dale Steele Efficent way to create an nxn upper triangular matrix of one's Feb 11 Sundar Dorai-Raj Efficent way to create an nxn upper triangular matrix of one's Feb 11 Jorge Ivan Velez Efficent way to create an nxn upper triangular matrix of one's Feb 11 Christos Hatzis Efficent way to create an nxn upper triangular matrix of one's Feb 11 David Winsemius Efficent way to create an nxn upper triangular matrix of one's Feb 13