This script will iteratively solve the Colebrook equation for the Darcy friction factor. Read more about it here: http://en.wikipedia.org/wiki/Colebrook_equation

Call this script from the command line like this: ./colebrook.m Re d epsilon

'Re' is the Reynolds number, 'epsilon' is the roughness height in millimeters, a characteristic of the pipe material that you can probably look up in published tables, depending on your requirements. 'd' is the pipe diameter in millimeters.

Try this:

./colebrook.m 25300 25.4 0.002;

This would represent a flow with Reynolds number 25300 in a 1-inch diameter smooth plastic pipe, for example.

This is very crudely done; for instance, 10 iterations is simply assumed to yield precise-enough results. Modify as needed. Attribution not necessary. Your mileage may vary.