Multiply each element in a vector by itself to cre

问题:

I'm trying to multiply each element in a vector by itself such that it produces a matrix that is symmetric about the diagonal. For example, given this vector::

x <- 1:3

I would like to create this:

1 2 3  
2 4 6 
3 6 9  

i.e:

x[1]*x[1] x[2]*x[1] x[3]*x[1]  
x[1]*x[2] x[2]*x[2] x[3]*x[2] 
x[1]*x[3] x[2]*x[3] x[3]*x[3] 

Any help would be greatly appreciated. Thanks.

回答1:

Like this:

x %o% x

which is a shortcut for

outer(x, x)

You can also do

 tcrossprod(x)