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;};var dnorm=function(x,mean,std){return 0.5*(1+erf((x-mean)/Math.sqrt(2*std*std)));}