Inlining

In Fortran double precision complex (i.e. where both the real part and the imaginary part are double precision numbers) is a built-in type. C does not have any complex type at all. A portable way of writing programs using C is to have separate arrays for the real- and imaginary parts and to implement complex arithmetic as procedures. It does not seem unreasonable, however, that this may slow things down, how much is what you are going to find out next:

Write a subroutine (void function in C)

subroutine mult ( re_a, im_a, re_b, im_b, re_c, im_c )

that computes the the product a = b * c where a, b and c are complex (a = a_re + sqrt(-1) * a_im etc.). Note that mult should work with scalars and not arrays (re_a, im_a etc. are scalars). Do the same even if you are using Fortran 90.

create six arrays re_a,im_a,re_b,im_b,re_c and im_c of length 10000 and use the routine above to form the product element by element (use a loop) using mult. repeat the loop 4000 times to get accurate measurements.

Important: store mult in a separate file.

Then inline mult, by hand, and run again.

Compare the times and draw conclusions. Explain what happens!