> Why do
> x<-b%*%ginv(A)
> and
> x<-solve(A,b)
> give different results?.
they do (in cases the solution to A x = b is unique):
R> A <- matrix(c(0,-4,4,0),nrow=2,ncol=2)
R> A
[,1] [,2]
[1,] 0 4
[2,] -4 0
R> b <- c(-16,0)
R> x1 <- ginv(A) %*% b <- NOT b %*% ginv(A)
R> x1
[,1]
[1,] 0
[2,] -4
R> x2 <- solve(A) %*% b
R> x2
[,1]
[1,] 0
[2,] -4
R> x3 <- solve(A, b)
R> x3
[1] 0 -4
Torsten
> It seems that I am missing some basic feature of
> matrix indexing.
> e.g.:
>
> A<-matrix(c(0,-4,4,0),nrow=2,ncol=2)
> b<-c(-16,0)
> x<-b%*%ginv(A);x
> x<-solve(A,b);x
>
> Thanks in advance,
> Angel
>
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