A = rbind( c(1,2,4), c(-1,2-8), c(7,0,1) )
A = rbind( c(1,2,4), c(-1,2,-8), c(7,0,1) )
A
det(A)
solve(A)
solve(A) %*%  A
solve(A) %*%  A  -> I
I
dig(I)
diag(I)
sum(diag(I))
A = cbind( c(1,2,4), c(-1,2,-8), c(7,0,1) )
A
A <- matrix( 1:9, c(3,3))
A
( A <- matrix( 1:9, c(3,3)) )
( A <- matrix( 1:6, c(2,3)) )
( A <- matrix( 1:6, c(3,2)) )
A
tA <- t(A)
tA
tA %*% A
A %*% tA
matrix(rep(NA, 9), c(3,3))
q()