function y = lorentz(v0,a,b,lambda)
%
% LORENTZ
%   y = lorentz(v0,a,b,lambda) returns a vector having
%   the same length as lambda and containing the values
%   of a Lorentzian-shaped curve with area = a over the
%   range of lambda.
%   The Lorentz curve is given by
%
%                        A
%          F(v) = --------------
%                  (v-v0)² + b²
%
%   The curve is a good approximation of the band shape of
%   Absorbance = log(Io/I) in infra-red absorption due to 
%   molecular vibrations.
%
%                                                    RJM 8/4/94
lambda = lambda(:);
k=length(lambda);
l1=atan((lambda(1)-v0)/b);
l2=atan((lambda(k)-v0)/b);
const=a*b/(l2-l1);
y=const*ones(k,1)./((lambda-v0).^2+b^2);