subroutine aptvuac (au, av, np, tol, vlen, nerr) ccbeg. cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc c c SUBROUTINE APTVUAC c c call aptvuac (au, av, np, tol, vlen, nerr) c c Version: aptvuac Updated 1990 November 26 10:00. c aptvuac Originated 1989 November 2 14:10. c c Author: Arthur L. Edwards, LLNL, L-298, Telephone (925) 422-4123. c c c Purpose: To find the np unit vectors a = (au, av) parallel to the np c initial vectors a = (au, av), all in the uv plane (2-D). Any c components of the initial vector "a" no greater than tol, or no c greater than tol times the initial length of "a", will be c truncated to zero. If all are zero, or are truncated to zero, c vlen will be zero. c Flag nerr indicates any input error. c c With no truncation, c (au, av) = (au, av) / sqrt (au**2 + av**2) c c History: 1990 March 14. Modified to always return a unit vector. c c Input: au, av, np, tol. c c Output: au, av, vlen, nerr. c c Glossary: c c au, av Input The u and v components of initial vector "a" in the c uv plane. Size np. c Will be truncated to zero if initially no greater c than tol, or no greater than tol times the initial c length of "a". c c au, av Output The u and v components of unit vector "a" in the c uv plane. Size np. c c nerr Output Indicates an input error, it not 0. c 1 if np is not positive. c c np Input Size of arrays au, av, vlen. c c tol Input Numerical tolerance limit. c On Cray computers, recommend 1.e-5 to 1.e-11. c c vlen Output Magnitude of the input vector "a", after any c truncation of components has been done, but before c division by vlen to form a unit vector. Size np. c cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc ccend. c.... Dimensioned arguments. c---- Component u of vector "a". dimension au (1) c---- Component v of vector "a". dimension av (1) c---- Magnitude of input vector "a". dimension vlen (1) c.... Local variables. c---- Square of estimated error in "a". common /laptvuac/ aerr2 c---- A very small number. common /laptvuac/ fuz c---- Index, 1 to np. common /laptvuac/ n cbugc***DEBUG begins. cbug 9901 format (/ 'aptvuac finding unit vectors with tol=',1pe13.5) cbug 9902 format (i3,' au,av= ',1p2e22.14) cbug write ( 3, 9901) tol cbug write ( 3, 9902) (n, au(n), av(n), n = 1, np) cbugc***DEBUG ends. c.... Initialize. c---- A very small number. fuz = 1.e-99 nerr = 0 c.... Test for input errors. if (np .le. 0) then nerr = 1 go to 210 endif c.... Test for the truncation option. c---- Truncate small components to zero. if (tol .gt. 0.0) then c---- Loop over vectors. do 110 n = 1, np aerr2 = tol**2 * amax1 (1.0, au(n)**2 + av(n)**2) if (au(n)**2 .lt. aerr2) then au(n) = 0.0 endif if (av(n)**2 .lt. aerr2) then av(n) = 0.0 endif c---- End of loop over vectors. 110 continue c---- Tested tol. endif c.... Find the unit vectors. c---- Loop over vectors. do 120 n = 1, np vlen(n) = sqrt (au(n)**2 + av(n)**2) au(n) = au(n) / (vlen(n) + fuz) av(n) = av(n) / (vlen(n) + fuz) c---- End of loop over vectors. 120 continue cbugc***DEBUG begins. cbug 9903 format (/ 'aptvuac results:' / cbug & (i3,' au,av,len=',1p3e22.14)) cbug write ( 3, 9903) (n, au(n), av(n), vlen(n), n = 1, np) cbugc***DEBUG ends. 210 return c.... End of subroutine aptvuac. (+1 line.) end UCRL-WEB-209832