Poissondist normc = new Poissondist(lambda);
sbeps=1.0e-12;
localflag=false;
for (i=1;i<20;i++) {
a=normc.cdf(i);
b=normc.invcdf(a);
localflag = localflag || (i-b != 0) && (i-b-1 != 0) ;
}
globalflag = globalflag || localflag;
if (localflag) {
fail("*** Poissondist: Inverse cdf does not accurately invert the cdf");