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: winding_number.m
    path of file: ./repos/gptoolbox/mex
    
    the code of the file until where you have to start completion: function [W] = winding_number(V,F,O,varargin)
  % WINDING_NUMBER Compute the sum of solid angles of a triangle (tetrahedron)
  % described by points (vectors) V
  % 
  % [W] = winding_number(V,F,O)
  % [W] = winding_number(V,F,O,'ParameterName',ParameterValue, ...)
  %
  % Inputs:
  %  V  #V by 3 list of vertex positions
  %  F  #F by 3 list of triangle indices
  %  O  #O by 3 list of origin positions
  %  Optional inputs:
  %    'Hierarchical'  followed by true or false. Use hierarchical evaluation.
  %      for mex: {true}, for matlab this is not supported 
  %    'Fast' followed by whether to use fast-winding-number {false}
  %    'RayCast' followed by true or flase. Use ray cast version of approximate
  %      evaluation: {false}
  %    'TwoDRays' followed by true or false. Use 2d rays only.
  %    'NumRays' followed by the number of rays to cast for each origin
  % Outputs:
  %  W  no by 1 list of winding numbers

    
function [W] = winding_number(V,F,O,varargin)
  % WINDING_NUMBER Compute the sum of solid angles of a triangle (tetrahedron)
  % described by points (vectors) V
  % 
  % [W] = winding_number(V,F,O)
  % [W] = winding_number(V,F,O,'ParameterName',ParameterValue, ...)
  %
  % Inputs:
  %  V  #V by 3 list of vertex positions
  %  F  #F by 3 list of triangle indices
  %  O  #O by 3 list of origin positions
  %  Optional inputs:
  %    'Hierarchical'  followed by true or false. Use hierarchical evaluation.
  %      for mex: {true}, for matlab this is not supported 
  %    'Fast' followed by whether to use fast-winding-number {false}
  %    'RayCast' followed by true or flase. Use ray cast version of approximate
  %      evaluation: {false}
  %    'TwoDRays' followed by true or false. Use 2d rays only.
  %    'NumRays' followed by the number of rays to cast for each origin
  % Outputs:
  %  W  no by 1 list of winding numbers
  %

  warning('not mex...');
  S = solid_angle(V,F,O);
  W = sum(S,2);
  switch size(F,2)
  case 3
    W = W/(2*pi);
  case 4
    W = W/(4*pi);
  end