Hello,

I have used Eigen a lot. But I am having a problem that I cannot understand.

Imagine this:

Code: Select all

int m = 40;
int n = 50;
ArrayXd s1 = ArrayXd::Ones(m);
MatrixXd m1 = MatrixXd::Random(n,m);

double sums = (m1.row(0).array()*s1).array().sum();    // this line doesn't work, WHY ?



Could you let me know how can I do a coefficient wise multiplication of a row of a column-major matrix with an array ?

Thanks

You are multiplying a row (1 x m) with a column array (m x 1), so you can do:

double sums = (m1.row(0).transpose().array()*s1).sum();

or:

sums = m1.row() * s1.matrix(); // classic inner product

or:

sums = m1.row().dot(s1.matrix());