Triangular matrix upper to down

Hi,
suppose that we have a triangular upper matrix A

test <- matrix(ncol = 4, nrow = 4)
test[1, ] <-  c(NA,1,1,1)
test[2, ] <-  c(NA,NA,1,1)
test[3, ] <-  c(NA,NA,NA,1)
test[4, ] <-  c(NA,NA,NA,NA)

I know how quickly set diagonal value diag(test) <- 1. But how quickly set
down value i.e. matrix is symmetrical? Is there in r project any quickly
function? 

Thanks,

Best 

Marcin

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