Speeding up numpy.dot

Question

I\'ve got a numpy script that spends about 50% of its runtime in the following code:

s = numpy.dot(v1, v1)

where

v1 = v[1

Answer 1

Your arrays are not very big, so ATLAS probably isn't doing much. What are your timings for the following Fortran program? Assuming ATLAS isn't doing much, this should give you a sense of how fast dot() could be if there was not any python overhead. With gfortran -O3 I get speeds of 5 +/- 0.5 us.

    program test

    real*8 :: x(4000), start, finish, s
    integer :: i, j
    integer,parameter :: jmax = 100000

    x(:) = 4.65
    s = 0.
    call cpu_time(start)
    do j=1,jmax
        s = s + dot_product(x, x)
    enddo
    call cpu_time(finish)
    print *, (finish-start)/jmax * 1.e6, s

    end program test