question: public double unsafeSabrVolatility ( final double strike , final double forward , final double expiryTime , final double alpha , final double beta , final double nu , final double rho ) { final double oneMinusBeta = 1.0 - beta ; final double A = Math . pow ( forward * strike , oneMinusBeta ) ; final double sqrtA = Math . sqrt ( A ) ; double logM ; if ( ! isClose ( forward , strike ) ) logM = Math . log ( forward / strike ) ; else { final double epsilon = ( forward - strike ) / strike ; logM = epsilon - .5 * epsilon * epsilon ; } final double z = ( nu / alpha ) * sqrtA * logM ; final double B = 1.0 - 2.0 * rho * z + z * z ; final double C = oneMinusBeta * oneMinusBeta * logM * logM ; final double tmp = ( Math . sqrt ( B ) + z - rho ) / ( 1.0 - rho ) ; final double xx = Math . log ( tmp ) ; final double D = sqrtA * ( 1.0 + C / 24.0 + C * C / 1920.0 ) ; final double d = 1.0 + expiryTime * ( oneMinusBeta * oneMinusBeta * alpha * alpha / ( 24.0 * A ) + 0.25 * rho * beta * nu * alpha / sqrtA + ( 2.0 - 3.0 * rho * rho ) * ( nu * nu / 24.0 ) ) ; double multiplier ; final double m = 10 ; if ( Math . abs ( z * z ) > Constants . QL_EPSILON * m ) multiplier = z / xx ; else { final double talpha = ( 0.5 - rho * rho ) / ( 1.0 - rho ) ; final double tbeta = alpha - .5 ; final double tgamma = rho / ( 1 - rho ) ; multiplier = 1.0 - beta * z + ( tgamma - talpha + tbeta * tbeta * .5 ) * z * z ; } return ( alpha / D ) * multiplier * d ; }
target:  Computes the Black equivalent volatility without validating parameters