B = -A 



IGT = 2 



GU TC 99 

 12 Mh\. = X - TQL 

 C START ITEKATICN LOUP 



IF ( VAL) 1,7,1 

 C EGUATION IS NCT SATISFIED bY X 



1 b = H/VAL - L.OOO 

 1F(B) Ztti,Z 



C ITEf^ATICN IS POSSIBLE 



2 A = A/0 • • 

 X = X + A 



B = VAL 

 TQL = X 

 IGT = 3 

 GG TC 99 

 2 3 VAL = X - TQL 

 C TEST Ci\| SATISFACTURY AGCURACY 



D = CAfiS (X ) 

 TOL = C,C0G8*D 



4 1^ I DABS(A)-TGL) 5,5,6 



5 IF(0A6S (VAL)-1.0nO*TL'L) 7,?, 6 



6 I F ( 1 - 20 ) 1 , 1 , lU 



C ENG CF ITERATICN LOOP 



7 C = C E X P ( X ) 

 RETURN 



C ERROR RETURN IN CASE OF ZERO DIVISOR 



6 lER = -2 

 RETURN 



C NC CGNVERGENCE AFTER 20 ITcRATIO.M LOOPS. ERROR RETURN 



10 lER = I 

 RETURN 



C ERRCR CCMCITION ON INITIAL ITERATION 



12 lER = -3 



RETURN 

 14 lER = -4 



RETURN 



100 GO TC ( 12,12, 102) , IGT 



101 GC TC ( 14, 14, 102 ), IGT 



102 X = X - A 



A = CIV*A/B 

 CIV = CIV*CIV 

 1 = 1 + 1 

 GO TC 2 

 END 



Figure 10. — FORTRAN subroutine to oaloulate relative productivity. 



The variables in the calling sequence are: 



Q = the measure of relative productivity 

 H = height in feet 



T = age in rings at 4.5 feet above ground 



18 



