Multiplication of matrices in R - problem of dimensions

Question

I am trying to multiply to matrices in R:

I know this multiplication can be done, but I am getting an error. Any idea why?

> d1
     [,1]
[1,]   -3
[2,]    0
[3,]    3

> t1
     [,1] [,2] [,3]
[1,]    2    2    2

> t1 * d1
Error in t1 * d1 : non-conformable arrays

I expect to got 0 from the multiplication – Sss Feb 03 '21 at 09:53 — Sss, Feb 03 '21 at 09:53

score 0 · Accepted Answer · answered Feb 03 '21 at 10:06

A few details more starting from @ThomasIsCoding comment:

d1<-as.matrix(c(-3,0,3))
t1<-t(as.matrix(c(2,2,2)))


d1 %*% t1
     [,1] [,2] [,3]
[1,]   -6   -6   -6
[2,]    0    0    0
[3,]    6    6    6

From the official CRAN documentation about matrix multiplication

A * B is the matrix of element by element products and

A %*% B is the matrix product.

If x is a vector, then

x %% A %% x is a quadratic form.

Link to the documenation HERE.

1 Answers1