The precision

[WarriorHanamy]

As far as I know, the precision of double float is around 1e-16, does the condition min_step = 1e-20 really works?

        /**
         * The minimum step of the line search routine.
         *  The default value is 1.0e-20. This value need not be modified unless
         *  the exponents are too large for the machine being used, or unless the
         *  problem is extremely badly scaled (in which case the exponents should
         *  be increased).
         */
        double min_step = 1.0e-20;