CODEWITHSUNDEEP
c++armadillo
Dr. Jekyll
Dr. Jekyll

Reputation: 406

Armadillo vector-matrix multiplication

Is it possible to multiply (dot product) a matrix by a vector in Armadillo ? It seems to me a basic operation we expect from this kind of library, so it should exist. All my attempts failed up to now:

"matrix multiplication: incompatible matrix dimensions: 1206x36 and 1x1206"
"matrix multiplication: incompatible matrix dimensions: 1206x36 and 1206x1"
"matrix multiplication: incompatible matrix dimensions: 1x1206 and 1206x36"
"matrix multiplication: incompatible matrix dimensions: 1206x1 and 1206x36"

Upvotes: 0

Views: 5294

Answers (1)

Patrick Kelly
Patrick Kelly

Reputation: 1381

Yes, it is possible. Can you provide a sample of the source code used to produce the errors above? Try the following, as it should work fine.

arma::mat X ;
arma::vec beta ;

beta.resize ( 2 ) ;

beta (0) = 1.0 ;
beta (1) = 3.0 ;

X.resize ( 3, 2 ) ;

X (0,0) = 1.0 ;
X (0,1) = 2.0 ;
X (1,0) = 3.0 ;
X (1,1) = 4.0 ;
X (2,0) = 5.0 ;
X (2,1) = 6.0 ;

std::cout << X * beta << std::endl ;

It will also work if both are defined as type "arma::mat", too, as long as the dimensions are compatible.

Upvotes: 3

Related Questions