EFcalc - Event/Fault Tree Calculator

Calculation Parameters File (*.cal) [optional]

Describes the user set calculation parameters. Comments may appear to the right of each number.

     0.0001   ! epsilon, how close to 1 or 0 to count as a house event
     15       ! nComcut, how many common variables before going MC
     2        ! istop,   MC stop criteria method, 1-4
     0.01     ! errmax,  MC stop criteria errmax
     1000     ! nHinit,  number of trials to start
     5000     ! nHmax,   maximum number of trials, no matter what
     13579    ! IX,      random seed (use large odd number)

Common house events (events that have failure probabilities identically equal to zero or one) are taken out of the list of common variables to speed up the calculation. The value epsilon describes how close to zero or one a probability must be in order to be considered a house event. This helps remove very small or very large probabilities from consideration. Recommended values are 0.0 to 0.001.

For problems with a small number of common variables, a direct solve will be used. For larger numbers of common variables, a Monte Carlo solution may be faster. nComcut fixes the number of common components where the Monte Carlo solution will be used instead of the direct solve. The recommended value is 15.

For Monte Carlo solutions, there are four different methods used for stopping criteria that the user can select. Each method (istop is 1 through 4) requires one number describing the maximum error (errmax). The stopping methods are:

     istop   stopping method
     1       absolute error on each sequence is below errmax
     2       absolute error on each consequence is below errmax
     3       relative error on each sequence is below errmax
     4       relative error on each consequence is below errmax

Relative error will be controlled by the smallest probability sequences, so use istop=3 or 4 with care, the errmax should not be set too low (less than 0.01) or long run times could result. When using the Monte Carlo solution, nHinit trials are run at the start. From these trials, an estimate of how many more trials are required to meet the stopping criteria is made. nHmax is the maximum number of trials to make, even if the stopping criteria is not met. This protects the user from long run times.

IX is the seed value for the random number generator. It is required to be a large odd number.

If the *.cal file is not present, default settings (the ones shown above) will be used and saved.

Oak Ridge National Laboratory, 2004

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