サブ　gamma.js　　　Last modified: Mar 25, 2004
function gamma(x)
{
  var a, b, z, factor, i, m, mg
   if (x > 171.6) {
       alert("gamma: Overflow./")
       return "Inf"
   }
   if (x <= 1.5) {
       if (x >= 0.5) {
           a = x-1.0
           factor = 1.0
       }
       else {
           m = Math.floor(x)
           a = x-m
           if (a == 0) {
               alert("gamma: Invalid argument./")
               return "Inf"
           }
           if (a >= -0.5) {
               mg = Math.abs(m)+1
           }
           else {
               mg = Math.abs(m)+2
               a++
           }
           z = 1.0
           for (i = 0; i < mg; i++) {
               z *= x
               x++
           }
           factor = 1.0/z
       }
   }
   else {
       m = Math.floor(x)
       a = x-m
       if (a <= 0.5) {
           mg = m-1
       }
       else {
           mg = m
           a--
       }
       z = 1.0
       for (i = 0; i < mg; i++) {
           z *= (x-1.0)
           x--
       }
       factor = z
   }
   b = ((((((((-0.42202e-11*a +0.120028e-10)*a +0.923397e-10)*a -0.12736143e-8)*a +0.62756218e-8)*a -0.1595268e-9)*a-0.2054743152e-6)*a +0.13385015466e-5)*a -0.25889950224e-5)*a
   b = ((((((((((b -0.175458597517e-4)*a +0.1455961421399e-3)*a -0.3608378162548e-3)*a -0.80432977560424699e-3)*a +0.80232730222673465e-2)*a -0.1764524455014432e-1)*a -0.24552490005400017e-1)*a +0.19109110138769151)*a -0.23309373642178674)*a -0.42278433509846714)*a +1.0
   return factor/(1.0+a)/b
}