NESC9659 FTAP.

1. NAME OR DESIGNATION OF PROGRAM:  FTAP.

3. DESCRIPTION OF PROBLEM OR FUNCTION

FTAP is a general-purpose program for deriving minimal reliability cut and path set families from the fault tree for a complex system. The program has a number of useful features that make it well-suited to nearly all fault tree applications. An input fault tree may specify the system state as any logical function of subsystem or component state variables or complements of these variables; thus, for instance, "exclusive-or" type relations may be formed. When fault tree logical relations involve complements of state variables, the analyst may instruct FTAP to produce a family of prime implicants, a generalization of the minimal cut set concept. The program offers the flexibility of several distinct methods of generating cut set families. FTAP can also identify certain subsystems as system modules and provide a collection of minimal cut set families that essentially expresses the system state as a function of these module state variables. Another feature allows a useful subfamily to be obtained when the family of minimal cut sets or prime implicants is too large to be found in its entirety; this subfamily may consist of only those sets not containing more than some fixed number of elements or only those sets "interesting" to the analyst in some special sense. Finally, the analyst can modify the input fault tree in various ways by declaring state variables identically true or false.

4. METHOD OF SOLUTION

Fault tree methods are based on the observation that the system state, either working or failed, can usually be expressed as a Boolean relation between states of several large, readily identifiable subsystems. The state of each subsystem in turn depends on states of simpler subsystems and components which compose it, so that the state of the system itself is determined by a hierarchy of logical relationships between states of subsystems. A fault tree is a graphical representation of these relationships.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

A linear work array  is used to adjust storage capacity depending on the size of trees.
The dimension of the array limits the complexity of the tree to be processed. The array bounds may be altered by changing the following two FORTRAN statements:

       COMMON IA (50000)
       DATA IASIZE /50000/

The value of 50000 is suitable for trees with about 100 components.
FTAP2 is the more efficient version and is recommended normally.
FTAP1 differs in internal data storage format and should be used for large trees.

6. TYPICAL RUNNING TIME

Very problem dependent.
NEA-DB required the following CPU times to run the test cases of the different programs in the package:
       FTAP:     1 sec
       FRTGEN:   1 sec
       FRELIB:   1 sec

7. UNUSUAL FEATURES OF THE PROGRAM

FTAP is available in two distinct  versions that differ only in the internal storage format for representing implicant sets. FTAP1 stores an implicant as a variable number of consecutive computer words in main memory. FTAP2 stores an implicant set as a fixed group of consecutive words, and a fault tree is associated with a unique bit position in one of these words. FTAP2 is the more efficient of the two versions in terms of computation time and should be chosen for most applications.

8. RELATED AND AUXILIARY PROGRAMS

For fault tree work, several features of FTAP are similar to features of the SETS program, NESC 623. In addition to fault tree analysis, SETS manipulates arbitrary  Boolean expressions.

Fault-Tree Generation and Design
                    for FTAP.
FRTPLT              FRTPLT - Fault-Tree Plot Program for FTAP.

10. REFERENCES

- Randall R. Willie
  Computer-Aided Fault Tree Analysis,
  UCRL-13981, August 1978, with Revisions.
- Test Examples for the Fault Tree Analysis Program,
  received July 1979.

- Program FRTGEN for Changing Fault Trees. (Paper)
- FRTPLT Program for Graphical Output of Fault Trees. (Paper).
- Randall R. Willie:
  Computer-Aided Fault Tree Analysis.  ORC 78-14  (August 1978)

11. MACHINE REQUIREMENTS

Hardware components normally used:
card reader, line printer, (card puncher), external disk or tape storage for three files.
Main storage requirements on IBM 3081 are as follows:
       FTAP version 1      720K bytes
       FTAP version 2      332K bytes
       FRTGEN              272K bytes
       FRELIB              156K bytes
       FTAIMP              156K bytes
       FTAP version 2
        FORTRAN routines   336K bytes

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  DOS/VS, CMS. MVS-SP (IBM 3081), SCOPE.

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

IBM versions of the six small assembler subroutines: ANDM, BCM, CCM, GETM, ORM, and PUTM, which perform several simple operations that cannot be done in the context of standard FORTRAN, are included. Specifications for these machine-language routines are contained in  the FTAP reference report, UCRL-13981, so that tey can be customized to both the computer and the FORTRAM compiler used.
NEA 0690/02: This version could only be compiled by NEA-DB on CDC 7600.
Adjust variable LWORD to length of computer word less one.
There is a call for SECOND to obtain CPU time from system.

15. NAME AND ESTABLISHMENT OF AUTHOR

Randall R. Willie
Lawrence Livermore National Laboratory

Willie's program was slightly modified with reference to the related programs FRTPLT, FRTGEN and IMPORTANCE by:

U. Rabien
Germanischer Lloyd
Vorsetzen 32
P.O. Box 11 16 06
2000 Hamburg 11
F.R. of Germany

File name	File description	Records
NESC9659_01.003	FTAP INFORMATION FILE	108
NESC9659_01.004	FTAP VERSION 1 SOURCE (FORTRAN-4)	4898
NESC9659_01.005	FTAP VERSION 2 SOURCE (FORTRAN-4)	5076
NESC9659_01.006	FTAP SOURCE (ASSEMBLER)	142
NESC9659_01.007	FTAP ALTERNATIVE VERSION (FORTRAN-4)	99
NESC9659_01.008	SECOND SOURCE (FORTRAN-4)	8
NESC9659_01.009	SECOND SOURCE (ASSEMBLER)	653
NESC9659_01.010	FTAIMP SOURCE (FORTRAN-4)	75
NESC9659_01.011	FTAP INPUT FOR TEST CASE 1	31
NESC9659_01.012	FTAP INPUT FOR TEST CASE 2	20
NESC9659_01.013	FTAIMP INPUT FOR TEST CASE	21
NESC9659_01.014	FTAP VERSION 1 OUTPUT OF TEST CASE 1	507
NESC9659_01.015	FTAP VERSION 1 OUTPUT OF TEST CASE 2	507
NESC9659_01.016	FTAP VERSION 2 OUTPUT OF TEST CASE 2	46
NESC9659_01.017	FTAP ALTERNATIVE VERSION TEST CASE OUTPUT	422
NESC9659_01.018	FTAIMP OUTPUT OF TEST CASE	27
NESC9659_01.019	FRTPLT SOURCE (FORTRAN-4)	1197
NESC9659_01.020	FRTGEN SOURCE (FORTRAN-4)	989
NESC9659_01.021	FRELIB SOURCE (FORTRAN-4)	241
NESC9659_01.022	FRTGEN INPUT FOR TEST CASE 1	43
NESC9659_01.023	FRTGEN OUTPUT OF TEST CASE 1	95
NESC9659_01.024	FRTGEN INPUT FOR TEST CASE 2	22
NESC9659_01.025	FRTGEN OUTPUT OF TEST CASE 2	88
NESC9659_01.026	FRELIB INPUT FOR TEST CASE	13
NESC9659_01.027	FRELIB OUTPUT OF TEST CASE	32
NESC9659_01.028	FRTPLT INPUT FOR TEST CASE	113
NESC9659_01.029	JCL	112