[R] Matrix multiplication ...

[Paul Gilbert]

>I know that %*% is used for matrix multiplication.  However, if I
>multiply t(Y) %*% Y, where Y is an n by 1 vector, then the product is
>a scalar.

No, it is a 1 x 1 matrix.  c(t(Y) %*% Y) is a scalar and should work:

> Y <- matrix(1:5,5,1)
> t(Y) %*% Y
     [,1]
[1,]   55
> is.matrix(t(Y) %*% Y)
[1] TRUE
> is.matrix(c(t(Y) %*% Y))
[1] FALSE

Paul Gilbert

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