Hello,

is there an efficient way to calculate the tensor product of two vectors (with the same dimension)?

thanks in advance,
David

Code: Select all

const int N=5;
Eigen::VectorXd a=Eigen::MatrixXd::Random(N);
Eigen::VectorXd b=Eigen::MatrixXd::Random(N);
Eigen::MatrixXd c(N,N);

for(int i=0;i<N;++i)
   for(int j=0;j<N;++j)
       c(i,j)=a(i)*b(j);


did I mention that Eigen is great?

that's a standard matrix product:

c = a * b;

and to avoid a temporary you can tell Eigen there is no aliasing:

c.noalias() = a * b;

Now that you mention it -- of course. Thank you.

What does aliasing mean? should I do it in any Mat-Mat product? I thought this lazy-evaluation stuff does it...?

best,
David

matrix products is the exception. This is to make sure that the common: X = X*X.adjoint; works fine.Using noalias makes sense only if you have the matrix product on the righ and side.