How large must an array be to make it worth calling the LAPACK
xAXPY routines?  How much performance gain is there over a standard
C loop?

make         # builds the executable time_axpy

./time_axpy  # steps through the computations.  Hit ctrl-c when you get bored;
             # timing data is written to STDOUT and the file results.txt (flushed
             # after each vector size)

make plot    # to show the BLAS v. C curves

