/* ndtri.c * * Inverse of Normal distribution function * * * * SYNOPSIS: * * double x, y, ndtri(); * * x = ndtri( y ); * * * * DESCRIPTION: * * Returns the argument, x, for which the area under the * Gaussian probability density function (integrated from * minus infinity to x) is equal to y. * * * For small arguments 0 < y < exp(-2), the program computes * z = sqrt( -2.0 * log(y) ); then the approximation is * x = z - log(z)/z - (1/z) P(1/z) / Q(1/z). * There are two rational functions P/Q, one for 0 < y < exp(-32) * and the other for y up to exp(-2). For larger arguments, * w = y - 0.5, and x/sqrt(2pi) = w + w**3 R(w**2)/S(w**2)). * * * ACCURACY: * * Relative error: * arithmetic domain # trials peak rms * DEC 0.125, 1 5500 9.5e-17 2.1e-17 * DEC 6e-39, 0.135 3500 5.7e-17 1.3e-17 * IEEE 0.125, 1 20000 7.2e-16 1.3e-16 * IEEE 3e-308, 0.135 50000 4.6e-16 9.8e-17 * * * ERROR MESSAGES: * * message condition value returned * ndtri domain x <= 0 -MAXNUM * ndtri domain x >= 1 MAXNUM * */ /* Cephes Math Library Release 2.1: January, 1989 Copyright 1984, 1987, 1989 by Stephen L. Moshier Direct inquiries to 30 Frost Street, Cambridge, MA 02140 */ #include #include "mconf.h" extern double MAXNUM; #ifdef UNK /* sqrt(2pi) */ static double s2pi = 2.50662827463100050242E0; #endif #ifdef DEC static unsigned short s2p[] = { 0040440, 0066230, 0177661, 0034055 }; #define s2pi *(double *)s2p #endif #ifdef IBMPC static unsigned short s2p[] = { 0x2706, 0x1ff6, 0x0d93, 0x4004 }; #define s2pi *(double *)s2p #endif #ifdef MIEEE static unsigned short s2p[] = { 0x4004, 0x0d93, 0x1ff6, 0x2706 }; #define s2pi *(double *)s2p #endif /* approximation for 0 <= |y - 0.5| <= 3/8 */ #ifdef UNK static double P0[5] = { -5.99633501014107895267E1, 9.80010754185999661536E1, -5.66762857469070293439E1, 1.39312609387279679503E1, -1.23916583867381258016E0, }; static double Q0[8] = { /* 1.00000000000000000000E0,*/ 1.95448858338141759834E0, 4.67627912898881538453E0, 8.63602421390890590575E1, -2.25462687854119370527E2, 2.00260212380060660359E2, -8.20372256168333339912E1, 1.59056225126211695515E1, -1.18331621121330003142E0, }; #endif #ifdef DEC static unsigned short P0[20] = { 0141557, 0155170, 0071360, 0120550, 0041704, 0000214, 0172417, 0067307, 0141542, 0132204, 0040066, 0156723, 0041136, 0163161, 0157276, 0007747, 0140236, 0116374, 0073666, 0051764, }; static unsigned short Q0[32] = { /*0040200,0000000,0000000,0000000,*/ 0040372, 0026256, 0110403, 0123707, 0040625, 0122024, 0020277, 0026661, 0041654, 0134161, 0124134, 0007244, 0142141, 0073162, 0133021, 0131371, 0042110, 0041235, 0043516, 0057767, 0141644, 0011417, 0036155, 0137305, 0041176, 0076556, 0004043, 0125430, 0140227, 0073347, 0152776, 0067251, }; #endif #ifdef IBMPC static unsigned short P0[20] = { 0x142d, 0x0e5e, 0xfb4f, 0xc04d, 0xedd9, 0x9ea1, 0x8011, 0x4058, 0xdbba, 0x8806, 0x5690, 0xc04c, 0xc1fd, 0x3bd7, 0xdcce, 0x402b, 0xca7e, 0x8ef6, 0xd39f, 0xbff3, }; static unsigned short Q0[36] = { /*0x0000,0x0000,0x0000,0x3ff0,*/ 0x74f9, 0xd220, 0x4595, 0x3fff, 0xe5b6, 0x8417, 0xb482, 0x4012, 0x81d4, 0x350b, 0x970e, 0x4055, 0x365f, 0x56c2, 0x2ece, 0xc06c, 0xcbff, 0xa8e9, 0x0853, 0x4069, 0xb7d9, 0xe78d, 0x8261, 0xc054, 0x7563, 0xc104, 0xcfad, 0x402f, 0xcdd5, 0xfabf, 0xeedc, 0xbff2, }; #endif #ifdef MIEEE static unsigned short P0[20] = { 0xc04d, 0xfb4f, 0x0e5e, 0x142d, 0x4058, 0x8011, 0x9ea1, 0xedd9, 0xc04c, 0x5690, 0x8806, 0xdbba, 0x402b, 0xdcce, 0x3bd7, 0xc1fd, 0xbff3, 0xd39f, 0x8ef6, 0xca7e, }; static unsigned short Q0[32] = { /*0x3ff0,0x0000,0x0000,0x0000,*/ 0x3fff, 0x4595, 0xd220, 0x74f9, 0x4012, 0xb482, 0x8417, 0xe5b6, 0x4055, 0x970e, 0x350b, 0x81d4, 0xc06c, 0x2ece, 0x56c2, 0x365f, 0x4069, 0x0853, 0xa8e9, 0xcbff, 0xc054, 0x8261, 0xe78d, 0xb7d9, 0x402f, 0xcfad, 0xc104, 0x7563, 0xbff2, 0xeedc, 0xfabf, 0xcdd5, }; #endif /* Approximation for interval z = sqrt(-2 log y ) between 2 and 8 * i.e., y between exp(-2) = .135 and exp(-32) = 1.27e-14. */ #ifdef UNK static double P1[9] = { 4.05544892305962419923E0, 3.15251094599893866154E1, 5.71628192246421288162E1, 4.40805073893200834700E1, 1.46849561928858024014E1, 2.18663306850790267539E0, -1.40256079171354495875E-1, -3.50424626827848203418E-2, -8.57456785154685413611E-4, }; static double Q1[8] = { /* 1.00000000000000000000E0,*/ 1.57799883256466749731E1, 4.53907635128879210584E1, 4.13172038254672030440E1, 1.50425385692907503408E1, 2.50464946208309415979E0, -1.42182922854787788574E-1, -3.80806407691578277194E-2, -9.33259480895457427372E-4, }; #endif #ifdef DEC static unsigned short P1[36] = { 0040601, 0143074, 0150744, 0073326, 0041374, 0031554, 0113253, 0146016, 0041544, 0123272, 0012463, 0176771, 0041460, 0051160, 0103560, 0156511, 0041152, 0172624, 0117772, 0030755, 0040413, 0170713, 0151545, 0176413, 0137417, 0117512, 0022154, 0131671, 0137017, 0104257, 0071432, 0007072, 0135540, 0143363, 0063137, 0036166, }; static unsigned short Q1[32] = { /*0040200,0000000,0000000,0000000,*/ 0041174, 0075325, 0004736, 0120326, 0041465, 0110044, 0047561, 0045567, 0041445, 0042321, 0012142, 0030340, 0041160, 0127074, 0166076, 0141051, 0040440, 0046055, 0040745, 0150400, 0137421, 0114146, 0067330, 0010621, 0137033, 0175162, 0025555, 0114351, 0135564, 0122773, 0145750, 0030357, }; #endif #ifdef IBMPC static unsigned short P1[36] = { 0x8edb, 0x9a3c, 0x38c7, 0x4010, 0x7982, 0x92d5, 0x866d, 0x403f, 0x7fbf, 0x42a6, 0x94d7, 0x404c, 0x1ba9, 0x10ee, 0x0a4e, 0x4046, 0x463e, 0x93ff, 0x5eb2, 0x402d, 0xbfa1, 0x7a6c, 0x7e39, 0x4001, 0x9677, 0x448d, 0xf3e9, 0xbfc1, 0x41c7, 0xee63, 0xf115, 0xbfa1, 0xe78f, 0x6ccb, 0x18de, 0xbf4c, }; static unsigned short Q1[32] = { /*0x0000,0x0000,0x0000,0x3ff0,*/ 0xd41b, 0xa13b, 0x8f5a, 0x402f, 0x296f, 0x89ee, 0xb204, 0x4046, 0x461c, 0x228c, 0xa89a, 0x4044, 0xd845, 0x9d87, 0x15c7, 0x402e, 0xba20, 0xa83c, 0x0985, 0x4004, 0x0232, 0xcddb, 0x330c, 0xbfc2, 0xb31d, 0x456d, 0x7f4e, 0xbfa3, 0x061e, 0x797d, 0x94bf, 0xbf4e, }; #endif #ifdef MIEEE static unsigned short P1[36] = { 0x4010, 0x38c7, 0x9a3c, 0x8edb, 0x403f, 0x866d, 0x92d5, 0x7982, 0x404c, 0x94d7, 0x42a6, 0x7fbf, 0x4046, 0x0a4e, 0x10ee, 0x1ba9, 0x402d, 0x5eb2, 0x93ff, 0x463e, 0x4001, 0x7e39, 0x7a6c, 0xbfa1, 0xbfc1, 0xf3e9, 0x448d, 0x9677, 0xbfa1, 0xf115, 0xee63, 0x41c7, 0xbf4c, 0x18de, 0x6ccb, 0xe78f, }; static unsigned short Q1[32] = { /*0x3ff0,0x0000,0x0000,0x0000,*/ 0x402f, 0x8f5a, 0xa13b, 0xd41b, 0x4046, 0xb204, 0x89ee, 0x296f, 0x4044, 0xa89a, 0x228c, 0x461c, 0x402e, 0x15c7, 0x9d87, 0xd845, 0x4004, 0x0985, 0xa83c, 0xba20, 0xbfc2, 0x330c, 0xcddb, 0x0232, 0xbfa3, 0x7f4e, 0x456d, 0xb31d, 0xbf4e, 0x94bf, 0x797d, 0x061e, }; #endif /* Approximation for interval z = sqrt(-2 log y ) between 8 and 64 * i.e., y between exp(-32) = 1.27e-14 and exp(-2048) = 3.67e-890. */ #ifdef UNK static double P2[9] = { 3.23774891776946035970E0, 6.91522889068984211695E0, 3.93881025292474443415E0, 1.33303460815807542389E0, 2.01485389549179081538E-1, 1.23716634817820021358E-2, 3.01581553508235416007E-4, 2.65806974686737550832E-6, 6.23974539184983293730E-9, }; static double Q2[8] = { /* 1.00000000000000000000E0,*/ 6.02427039364742014255E0, 3.67983563856160859403E0, 1.37702099489081330271E0, 2.16236993594496635890E-1, 1.34204006088543189037E-2, 3.28014464682127739104E-4, 2.89247864745380683936E-6, 6.79019408009981274425E-9, }; #endif #ifdef DEC static unsigned short P2[36] = { 0040517, 0033507, 0036236, 0125641, 0040735, 0044616, 0014473, 0140133, 0040574, 0012567, 0114535, 0102541, 0040252, 0120340, 0143474, 0150135, 0037516, 0051057, 0115361, 0031211, 0036512, 0131204, 0101511, 0125144, 0035236, 0016627, 0043160, 0140216, 0033462, 0060512, 0060141, 0010641, 0031326, 0062541, 0101304, 0077706, }; static unsigned short Q2[32] = { /*0040200,0000000,0000000,0000000,*/ 0040700, 0143322, 0132137, 0040501, 0040553, 0101155, 0053221, 0140257, 0040260, 0041071, 0052573, 0010004, 0037535, 0066472, 0177261, 0162330, 0036533, 0160475, 0066666, 0036132, 0035253, 0174533, 0027771, 0044027, 0033502, 0016147, 0117666, 0063671, 0031351, 0047455, 0141663, 0054751, }; #endif #ifdef IBMPC static unsigned short P2[36] = { 0xd574, 0xe793, 0xe6e8, 0x4009, 0x780b, 0xc327, 0xa931, 0x401b, 0xb0ac, 0xf32b, 0x82ae, 0x400f, 0x9a0c, 0x18e7, 0x541c, 0x3ff5, 0x2651, 0xf35e, 0xca45, 0x3fc9, 0x354d, 0x9069, 0x5650, 0x3f89, 0x1812, 0xe8ce, 0xc3b2, 0x3f33, 0x2234, 0x4c0c, 0x4c29, 0x3ec6, 0x8ff9, 0x3058, 0xccac, 0x3e3a, }; static unsigned short Q2[32] = { /*0x0000,0x0000,0x0000,0x3ff0,*/ 0xe828, 0x568b, 0x18da, 0x4018, 0x3816, 0xaad2, 0x704d, 0x400d, 0x6200, 0x2aaf, 0x0847, 0x3ff6, 0x3c9b, 0x5fd6, 0xada7, 0x3fcb, 0xc78b, 0xadb6, 0x7c27, 0x3f8b, 0x2903, 0x65ff, 0x7f2b, 0x3f35, 0xccf7, 0xf3f6, 0x438c, 0x3ec8, 0x6b3d, 0xb876, 0x29e5, 0x3e3d, }; #endif #ifdef MIEEE static unsigned short P2[36] = { 0x4009, 0xe6e8, 0xe793, 0xd574, 0x401b, 0xa931, 0xc327, 0x780b, 0x400f, 0x82ae, 0xf32b, 0xb0ac, 0x3ff5, 0x541c, 0x18e7, 0x9a0c, 0x3fc9, 0xca45, 0xf35e, 0x2651, 0x3f89, 0x5650, 0x9069, 0x354d, 0x3f33, 0xc3b2, 0xe8ce, 0x1812, 0x3ec6, 0x4c29, 0x4c0c, 0x2234, 0x3e3a, 0xccac, 0x3058, 0x8ff9, }; static unsigned short Q2[32] = { /*0x3ff0,0x0000,0x0000,0x0000,*/ 0x4018, 0x18da, 0x568b, 0xe828, 0x400d, 0x704d, 0xaad2, 0x3816, 0x3ff6, 0x0847, 0x2aaf, 0x6200, 0x3fcb, 0xada7, 0x5fd6, 0x3c9b, 0x3f8b, 0x7c27, 0xadb6, 0xc78b, 0x3f35, 0x7f2b, 0x65ff, 0x2903, 0x3ec8, 0x438c, 0xf3f6, 0xccf7, 0x3e3d, 0x29e5, 0xb876, 0x6b3d, }; #endif double ndtri (double y0) { double x, y, z, y2, x0, x1; int code; if (y0 <= 0.0) { mtherr ("ndtri", MATHERR_DOMAIN); return (-MAXNUM); } if (y0 >= 1.0) { mtherr ("ndtri", MATHERR_DOMAIN); return (MAXNUM); } code = 1; y = y0; if (y > (1.0 - 0.13533528323661269189)) { /* 0.135... = exp(-2) */ y = 1.0 - y; code = 0; } if (y > 0.13533528323661269189) { y = y - 0.5; y2 = y * y; x = y + y * (y2 * polevl (y2, P0, 4) / p1evl (y2, Q0, 8)); x = x * s2pi; return (x); } x = sqrt (-2.0 * log (y)); x0 = x - log (x) / x; z = 1.0 / x; if (x < 8.0) /* y > exp(-32) = 1.2664165549e-14 */ x1 = z * polevl (z, P1, 8) / p1evl (z, Q1, 8); else x1 = z * polevl (z, P2, 8) / p1evl (z, Q2, 8); x = x0 - x1; if (code != 0) x = -x; return (x); }