% simple MATLAB/Octave program to simulate Mean Time Between Failures
Ns = 10000;          % number of simulations
Np = 3;              % number of parts in product
mu = [11 12 13];     % mean life span of every part
sigma = [1 2 3];     % standard deviation for each part
sample = [0 0 0];    % allocate memory for samples
m = 0; s = 0;        % mean and standard deviation for product
for i=1:Ns           % randn samples for normal distribution
  for j=1:Np         % with mean 0 and standard deviation 1
     sample(j) = mu(j) + sigma(j)*randn;
  end;
  t = min(sample);   % product fails if one of its components fails
  m = m + t/Ns;      % update mean life span for the product
  s = s + t^2/Ns;    % update the second moment
end; 
m                    % report the mean life span of product
s = sqrt(s - m*m)    % standard deviation of life span