| 1 |
gezelter |
2756 |
! ********************************************************************** |
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! erfc.F used with permission from Naval Surface Warfare Group |
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!****************************************************************************** |
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function erfc (x) |
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use definitions |
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!! ERFC: the complementary error function |
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real( kind = DP ) :: erfc |
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real( kind = DP ) :: an, ax, c, eps, rpinv, t, x, w |
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real( kind = DP ) :: a(21), b(44), e(44) |
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real( kind = DP ) :: dpmpar, dcsevl |
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! |
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! rpinv = 1/sqrt(pi) |
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! |
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data rpinv /.56418958354775628694807945156077259e0_dp/ |
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! |
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data a(1) / .1283791670955125738961589031215e+00_dp/, & |
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a(2) /-.3761263890318375246320529677070e+00_dp/, & |
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a(3) / .1128379167095512573896158902931e+00_dp/, & |
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a(4) /-.2686617064513125175943235372542e-01_dp/, & |
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a(5) / .5223977625442187842111812447877e-02_dp/, & |
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a(6) /-.8548327023450852832540164081187e-03_dp/, & |
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a(7) / .1205533298178966425020717182498e-03_dp/, & |
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a(8) /-.1492565035840625090430728526820e-04_dp/, & |
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a(9) / .1646211436588924261080723578109e-05_dp/, & |
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a(10) /-.1636584469123468757408968429674e-06_dp/ |
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data a(11) / .1480719281587021715400818627811e-07_dp/, & |
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a(12) /-.1229055530145120140800510155331e-08_dp/, & |
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a(13) / .9422759058437197017313055084212e-10_dp/, & |
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a(14) /-.6711366740969385085896257227159e-11_dp/, & |
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a(15) / .4463222608295664017461758843550e-12_dp/, & |
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a(16) /-.2783497395542995487275065856998e-13_dp/, & |
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a(17) / .1634095572365337143933023780777e-14_dp/, & |
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a(18) /-.9052845786901123985710019387938e-16_dp/, & |
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a(19) / .4708274559689744439341671426731e-17_dp/, & |
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a(20) /-.2187159356685015949749948252160e-18_dp/, & |
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a(21) / .7043407712019701609635599701333e-20_dp/ |
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! |
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data b(1) / .610143081923200417926465815756e+00_dp/, & |
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b(2) /-.434841272712577471828182820888e+00_dp/, & |
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b(3) / .176351193643605501125840298123e+00_dp/, & |
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b(4) /-.607107956092494148600512158250e-01_dp/, & |
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b(5) / .177120689956941144861471411910e-01_dp/, & |
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b(6) /-.432111938556729381859986496800e-02_dp/, & |
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b(7) / .854216676887098678819832055000e-03_dp/, & |
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b(8) /-.127155090609162742628893940000e-03_dp/, & |
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b(9) / .112481672436711894688470720000e-04_dp/, & |
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b(10) / .313063885421820972630152000000e-06_dp/ |
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data b(11) /-.270988068537762022009086000000e-06_dp/, & |
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b(12) / .307376227014076884409590000000e-07_dp/, & |
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b(13) / .251562038481762293731400000000e-08_dp/, & |
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b(14) /-.102892992132031912759000000000e-08_dp/, & |
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b(15) / .299440521199499393630000000000e-10_dp/, & |
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b(16) / .260517896872669362900000000000e-10_dp/, & |
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b(17) /-.263483992417196938600000000000e-11_dp/, & |
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b(18) /-.643404509890636443000000000000e-12_dp/, & |
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b(19) / .112457401801663447000000000000e-12_dp/, & |
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b(20) / .172815333899860980000000000000e-13_dp/ |
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data b(21) /-.426410169494237500000000000000e-14_dp/, & |
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b(22) /-.545371977880191000000000000000e-15_dp/, & |
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b(23) / .158697607761671000000000000000e-15_dp/, & |
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b(24) / .208998378443340000000000000000e-16_dp/, & |
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b(25) /-.590052686940900000000000000000e-17_dp/, & |
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b(26) /-.941893387554000000000000000000e-18_dp/, & |
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b(27) / .214977356470000000000000000000e-18_dp/, & |
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b(28) / .466609850080000000000000000000e-19_dp/, & |
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b(29) /-.724301186200000000000000000000e-20_dp/, & |
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b(30) /-.238796682400000000000000000000e-20_dp/ |
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data b(31) / .191177535000000000000000000000e-21_dp/, & |
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b(32) / .120482568000000000000000000000e-21_dp/, & |
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b(33) /-.672377000000000000000000000000e-24_dp/, & |
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b(34) /-.574799700000000000000000000000e-23_dp/, & |
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b(35) /-.428493000000000000000000000000e-24_dp/, & |
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b(36) / .244856000000000000000000000000e-24_dp/, & |
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b(37) / .437930000000000000000000000000e-25_dp/, & |
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b(38) /-.815100000000000000000000000000e-26_dp/, & |
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b(39) /-.308900000000000000000000000000e-26_dp/, & |
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b(40) / .930000000000000000000000000000e-28_dp/ |
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data b(41) / .174000000000000000000000000000e-27_dp/, & |
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b(42) / .160000000000000000000000000000e-28_dp/, & |
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b(43) /-.800000000000000000000000000000e-29_dp/, & |
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b(44) /-.200000000000000000000000000000e-29_dp/ |
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! |
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data e(1) / .107797785207238315116833591035e+01_dp/, & |
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e(2) /-.265598904091486733721465009040e-01_dp/, & |
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e(3) /-.148707314669809950960504633300e-02_dp/, & |
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e(4) /-.138040145414143859607708920000e-03_dp/, & |
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e(5) /-.112803033322874914985073660000e-04_dp/, & |
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e(6) /-.117286984274372522405373900000e-05_dp/, & |
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e(7) /-.103476150393304615537382000000e-06_dp/, & |
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e(8) /-.118991140858924382544470000000e-07_dp/, & |
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e(9) /-.101622254498949864047600000000e-08_dp/, & |
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e(10) /-.137895716146965692169000000000e-09_dp/ |
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data e(11) /-.936961303373730333500000000000e-11_dp/, & |
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e(12) /-.191880958395952534900000000000e-11_dp/, & |
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e(13) /-.375730172019937070000000000000e-13_dp/, & |
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e(14) /-.370537260269833570000000000000e-13_dp/, & |
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e(15) / .262756542349037100000000000000e-14_dp/, & |
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e(16) /-.112132287643793300000000000000e-14_dp/, & |
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e(17) / .184136028922538000000000000000e-15_dp/, & |
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e(18) /-.491302565748860000000000000000e-16_dp/, & |
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e(19) / .107044551673730000000000000000e-16_dp/, & |
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e(20) /-.267189366240500000000000000000e-17_dp/ |
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data e(21) / .649326867976000000000000000000e-18_dp/, & |
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e(22) /-.165399353183000000000000000000e-18_dp/, & |
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e(23) / .426056266040000000000000000000e-19_dp/, & |
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e(24) /-.112558407650000000000000000000e-19_dp/, & |
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e(25) / .302561744800000000000000000000e-20_dp/, & |
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e(26) /-.829042146000000000000000000000e-21_dp/, & |
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e(27) / .231049558000000000000000000000e-21_dp/, & |
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e(28) /-.654695110000000000000000000000e-22_dp/, & |
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e(29) / .188423140000000000000000000000e-22_dp/, & |
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e(30) /-.550434100000000000000000000000e-23_dp/ |
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data e(31) / .163095000000000000000000000000e-23_dp/, & |
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e(32) /-.489860000000000000000000000000e-24_dp/, & |
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e(33) / .149054000000000000000000000000e-24_dp/, & |
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e(34) /-.459220000000000000000000000000e-25_dp/, & |
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e(35) / .143180000000000000000000000000e-25_dp/, & |
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e(36) /-.451600000000000000000000000000e-26_dp/, & |
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e(37) / .144000000000000000000000000000e-26_dp/, & |
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e(38) /-.464000000000000000000000000000e-27_dp/, & |
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e(39) / .151000000000000000000000000000e-27_dp/, & |
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e(40) /-.500000000000000000000000000000e-28_dp/ |
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data e(41) / .170000000000000000000000000000e-28_dp/, & |
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e(42) /-.600000000000000000000000000000e-29_dp/, & |
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e(43) / .200000000000000000000000000000e-29_dp/, & |
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e(44) /-.100000000000000000000000000000e-29_dp/ |
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! |
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eps = epsilon ( eps ) |
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! |
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! abs(x) <= 1 |
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! |
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ax = abs(x) |
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if (ax > 1.0_dp) go to 20 |
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t = x*x |
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w = a(21) |
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do i = 1,20 |
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k = 21 - i |
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w = t*w + a(k) |
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end do |
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erfc = 0.5_dp + (0.5_dp - x*(1.0_dp + w)) |
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return |
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! |
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! 1 < abs(x) < 2 |
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! |
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20 if (ax >= 2.0_dp) go to 30 |
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n = 44 |
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if (eps >= 1.0e-20_dp) n = 30 |
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t = (ax - 3.75_dp)/(ax + 3.75_dp) |
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erfc = csevl(t, b, n) |
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21 erfc = exp(-x*x) * erfc |
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if (x < 0.0_dp) erfc = 2.0_dp - erfc |
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return |
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! |
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! 2 < dabs(x) < 12 |
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! |
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30 if (x < -9.0_dp) go to 60 |
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if (x >= 12.0_dp) go to 40 |
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n = 44 |
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if (eps >= 1.0e-20_dp) n = 25 |
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t = (1.0_dp/x)**2 |
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w = (10.5_dp*t - 1.0_dp)/(2.5_dp*t + 1.0_dp) |
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erfc = csevl(w, e, n) / ax |
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go to 21 |
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! |
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! x >= 12 |
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! |
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40 if (x > 50.0_dp) go to 70 |
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t = (1.0_dp/x)**2 |
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an = -0.5_dp |
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c = 0.5_dp |
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w = 0.0_dp |
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50 c = c + 1.0_dp |
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an = - c*an*t |
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w = w + an |
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if (abs(an) > eps) go to 50 |
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w = (-0.5_dp + w)*t + 1.0_dp |
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erfc = exp(-x*x) * ((rpinv*w)/ax) |
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return |
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! |
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! limit value for large negative x |
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! |
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60 erfc = 2.0_dp |
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return |
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! |
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! limit value for large positive x |
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! |
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70 erfc = 0.0_dp |
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return |
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end function erfc |
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function csevl (x, a, n) |
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!! CSEVL: evaluate the n term chebyshev series a at x. |
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!! only half of the first coefficient is used. |
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use definitions |
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real( kind = DP ) :: csevl |
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real( kind = DP ) :: a(n), x, x2, s0, s1, s2 |
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if (n .le. 1) then |
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csevl = 0.5_dp * a(1) |
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return |
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else |
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| 209 |
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x2 = x + x |
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s0 = a(n) |
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s1 = 0.0_dp |
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do i = 2,n |
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s2 = s1 |
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s1 = s0 |
| 215 |
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k = n - i + 1 |
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s0 = x2*s1 - s2 + a(k) |
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end do |
| 218 |
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csevl = 0.5_dp * (s0 - s2) |
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return |
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endif |
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end function csevl |
