question: public static double cdf ( double x , double mu , double shape ) { if ( ! ( x > 0. ) ) { return 0. ; } final double v0 = x / mu ; final double v1 = Math . sqrt ( shape / x ) ; if ( v1 == 0. ) { return v0 > 0. ? 1 : 0. ; } double c1 = NormalDistribution . standardNormalCDF ( v1 * ( v0 - 1. ) ) ; double c2 = NormalDistribution . standardNormalCDF ( - v1 * ( v0 + 1. ) ) ; return ( c2 > 0. ) ? c1 + Math . exp ( 2 * shape / mu ) * c2 : c1 ; }
target:  Cumulative probability density function (CDF) of a Wald distribution.