colebrook.m

% F = COLEBROOK(R,K) fast, accurate and robust computation of the
% Darcy-Weisbach friction factor F according to the Colebrook equation:
% - -
% 1 | K 2.51 |
% --------- = -2 * Log_10 | ----- + ------------- |
% sqrt(F) | 3.7 R * sqrt(F) |
% - -
% INPUT:
% R : Reynolds' number (should be >= 2300).
% K : Equivalent sand roughness height divided by the hydraulic
% diameter (default K=0).
%
% OUTPUT:
% F : Friction factor.
%
% FORMAT:
% R, K and F are either scalars or compatible arrays.
%
% ACCURACY:
% Around machine precision forall R > 3 and forall K>=0,
% i.e. forall values of physical interest.
%
% EXAMPLE: F = colebrook([3e3,7e5,1e100],0.01)

This m-file is more efficient than the solution of the Colebrook equation via the Lambert W-function, or the simple approximations.

PS: For the first submission of this m-file, the author accidentaly uploaded a test version. This resubmission should be the correct one.