C #XCOEFF V1A 15-FEB-72. C LAST UPDATE: C FUNCTION XCOEFF(J1,J2,J3,J4,J5,J6,J7,J8,J9) C C *PURPOSE. C TO EVALUATE THE "X" OR "9-J" RECOUPLING COEFFICIENT C AS DEFINED IN ANY STANDARD TEXT ON ANGULAR MOMENTUM. C C *PARAMETERS: C C J1 - INTEGER FIRST ANGULAR MOMENTUM QU-NR. C J2 - SECOND C J3 - THIRD C J4 - FOURTH C J5 - FIFTH C J6 - SIXTH C J7 - SEVENTH C J8 - EIGHTH C J9 - NINTH. C C NOTE!! BY CONVENTION ALL ANGULAR MOMENTUM QUANTUM NUMBERS ARE C INTEGERS WITH TWICE THEIR PHYSICAL VALUE. THIS APPLIES TO C ALL THE PARAMETERS ABOVE. WHEN WRITTEN AS A 9-J SYMBOL C THE ORDERING OF THE J'S IS EITHER: C C J1 J2 J3 J1 J4 J7 C J4 J5 J6 J2 J5 J8 C J7 J8 J9 J3 J6 J9 C C THESE GIVING IDENTICAL VALUES. C C INPUT PARAMETERS: C J1, J2, J3, J4, J5, J6, J7, J8, J9 C OUTPUT PARAMETERS: C (ONLY THE REAL FUNCTION VALUE) C C *METHOD. C THE STANDARD FORMULA DEFINING THE X-COEFFICIENT IN TERMS C OF A SUM OF PRODUCTS OF RACAH COEFFICIENTS IS USED. NOTE THAT C THIS VERSION HAS NO TEST FOR THE MANY SIMPLE CASES OF X-COEFF C WHICH CAN BE EVALUATED MORE QUICKLY. C C *ACCURACY. C C *RESTRICTIONS. C C *ERROR CONDITIONS. C THE VALUE ZERO WILL BE RETURNED FOR NON PHYSICAL COMBINATIONS C OF QUANTUM NUMBERS. C C *NON STANDARD ROUTINES CALLED. C RACAH - RACAH OR 6-J COEFFICIENT - MRMLIB. C C *TYPICAL TIMES. C C *ORIGIN. M.R.MANNING. C C *COMMENTS. C C #END. C IND=MIN0(J1+J9,J8+J4,J2+J6) IST=MAX0(IABS(J1-J9),IABS(J4-J8),IABS(J2-J6) ) XCOEFF=0. DO 10 I=IST,IND,2 10 XCOEFF= XCOEFF + FLOAT(I+1)*RACAH(J1,J9,J2,J6,I,J3)* 1 RACAH(J2,J6,J8,J4,I,J5)*RACAH(J8,J4,J9,J1,I,J7) C RETURN END