You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spm_Ncdf_jdw.m
    path of file: ./repos/spm
    
    the code of the file until where you have to start completion: function F = spm_Ncdf_jdw(x,u,v)
% Cumulative Distribution Function (CDF) for univariate Normal distributions: J.D.  Williams approximation
% FORMAT F = spm_Ncdf_jdw(x,u,v)

    
function F = spm_Ncdf_jdw(x,u,v)
% Cumulative Distribution Function (CDF) for univariate Normal distributions: J.D.  Williams approximation
% FORMAT F = spm_Ncdf_jdw(x,u,v)
%
% x - ordinates
% u - mean              [Defaults to 0]
% v - variance  (v>0)   [Defaults to 1]
% F - pdf of N(u,v) at x (Lower tail probability)
%__________________________________________________________________________
%
% spm_Ncdf implements the Cumulative Distribution Function (CDF) for
% the Normal (Gaussian) family of distributions.
%
% References:
%--------------------------------------------------------------------------
% An Approximation to the Probability Integral
% J. D. Williams 
% The Annals of Mathematical Statistics, Vol. 17, No. 3. (Sep., 1946), pp.
% 363-365. 
%
%__________________________________________________________________________

% Karl Friston
% Copyright (C) 2008-2022 Wellcome Centre for Human Neuroimaging


%-Format arguments
%--------------------------------------------------------------------------
if nargin < 3, v = 1; end