code: function erf(x) {
          var cof = [-1.3026537197817094, 6.4196979235649026e-1, 1.9476473204185836e-2, -9.561514786808631e-3, -9.46595344482036e-4, 3.66839497852761e-4,
              4.2523324806907e-5, -2.0278578112534e-5, -1.624290004647e-6,
              1.303655835580e-6, 1.5626441722e-8, -8.5238095915e-8,
              6.529054439e-9, 5.059343495e-9, -9.91364156e-10, -2.27365122e-10, 9.6467911e-11, 2.394038e-12, -6.886027e-12, 8.94487e-13, 3.13092e-13, -1.12708e-13, 3.81e-16, 7.106e-15, -1.523e-15, -9.4e-17, 1.21e-16, -2.8e-17
          ];
          var j = cof.length - 1;
          var isneg = false;
          var d = 0;
          var dd = 0;
          var t, ty, tmp, res;
  
          if (x < 0) {
              x = -x;
              isneg = true;
          }
  
          t = 2 / (2 + x);
          ty = 4 * t - 2;
  
          for (; j > 0; j--) {
              tmp = d;
              d = ty * d - dd + cof[j];
              dd = tmp;
          }
  
          res = t * Math.exp(-x * x + 0.5 * (cof[0] + ty * d) - dd);
          return isneg ? res - 1 : 1 - res;
      }
docs: /*
  Error function
  
  The MIT License, Copyright (c) 2013 jStat