[ublas] prod() performance question

From: Gross, Steve (SGross_at_[hidden])
Date: 2007-03-22 11:13:10

I've been testing the performance of ublas's matrix multiplication. I
encountered a behavior that I don't quite understand. Consider the
following code snippet:

 

Ublas::matrix<double> m1(100, 100), C(100, 100);

Ublas::Prod(m1, m1)

c = ublas::prod(m1, m1)

 

The second line and the third line are identical, except that in the
third line I assign the result of the product operation to a pre-sized
matrix. The second line appears to take almost no time to execute (0
millisecs, that is). The third line takes a non-zero amount of time to
execute, however.

 

What's going on here? Is the product operation super crazy fast, but the
matrix assignment part slow?

 

--Steve