function retval = norm_pdf(x,mu,sigma)
% usage: y = norm_pdf(x,mu,sigma)
% description: returns the value of the normal
% probability density function with mean mu
% and standard deviation sigma at x.

% Contact: Tom Shores, tshores1@math.unl.edu 

retval = 1./exp((x-mu).^2/(2*sigma^2))/sqrt(2*pi)/sigma;
