Gamma function Input parameters: X - argument Domain: 0 < X < 171.6 -170 < X < 0, X is not an integer. Relative error: arithmetic domain # trials peak rms IEEE -170,-33 20000 2.3e-15 3.3e-16 IEEE -33, 33 20000 9.4e-16 2.2e-16 IEEE 33, 171.6 20000 2.3e-15 3.2e-16 Cephes Math Library Release 2.8
| 50 | Translated to AlgoPascal by Bochkanov Sergey (2005, 2006, 2007). |
| 51 | *************************************************************************/ |
| 52 | double gamma(double x) |
| 53 | { |
| 54 | #ifndef ALGLIB_INTERCEPTS_SPECFUNCS |
| 55 | double result; |
| 56 | double p; |
| 57 | double pp; |
| 58 | double q; |
| 59 | double qq; |
| 60 | double z; |
| 61 | int i; |
| 62 | double sgngam; |
| 63 | |
| 64 | sgngam = 1; |
| 65 | q = fabs(x); |
| 66 | if( ap::fp_greater(q,33.0) ) |
| 67 | { |
| 68 | if( ap::fp_less(x,0.0) ) |
| 69 | { |
| 70 | p = ap::ifloor(q); |
| 71 | i = ap::round_f(p); |
| 72 | if( i%2==0 ) |
| 73 | { |
| 74 | sgngam = -1; |
| 75 | } |
| 76 | z = q-p; |
| 77 | if( ap::fp_greater(z,0.5) ) |
| 78 | { |
| 79 | p = p+1; |
| 80 | z = q-p; |
| 81 | } |
| 82 | z = q*sin(ap::pi()*z); |
| 83 | z = fabs(z); |
| 84 | z = ap::pi()/(z*gammastirf(q)); |
| 85 | } |
| 86 | else |
| 87 | { |
| 88 | z = gammastirf(x); |
| 89 | } |
| 90 | result = sgngam*z; |
| 91 | return result; |
| 92 | } |
| 93 | z = 1; |
| 94 | while(ap::fp_greater_eq(x,3)) |
| 95 | { |
| 96 | x = x-1; |
| 97 | z = z*x; |
| 98 | } |
| 99 | while(ap::fp_less(x,0)) |
| 100 | { |
| 101 | if( ap::fp_greater(x,-0.000000001) ) |
| 102 | { |
| 103 | result = z/((1+0.5772156649015329*x)*x); |
| 104 | return result; |
| 105 | } |
| 106 | z = z/x; |
| 107 | x = x+1; |
| 108 | } |
| 109 | while(ap::fp_less(x,2)) |
no test coverage detected