function vf=boltvfcn(v)
%-----------------------------------------------------------------------
% Return the m-th moment of the Maxwell-Boltzmann distribution function
%   f(v)=4*pi*(xm/2/pi/xk/T)^1.5 * exp(-xm*v*v/2/xk/T)*v*v
% Given
%   v  = Speed (m/sec)
%   xm = Mass of molecule = 32 g/mole for oxygen
%   xk = Boltzmann (gas) constant = 8.319 Joule/mole-K
%   T  = Temperature (K)
%   moment = m-th moment
% Note: for moment=0, the integral of vf from 0 to infinity should be unity.
%           moment=1, the integral gives the mean speed.
%           moment=2, the squared root of the integral gives the root-mean speed.
%-----------------------------------------------------------------------
% Programming Note:
%   The integrand function must return a vector when the input v is a vector.
%   This is because MATLAB evaluates this function at many points of v; it
%   throws into this function a whole vector v (not just a scalar).
%-----------------------------------------------------------------------
      global xm
      global T moment

% Some constants
%     pi = 3.141593;
      xk = 8.319;   % Joule/mole-K

% Calculate the distribution function
      f = 4*pi*(xm/2/pi/xk/T)^1.5 * exp(-xm*v.*v/2/xk/T).*v.*v;
      vf = v.^moment.*f;