double y1( double t ) {
    double tm{ t - 1.0 };
    return 0.62665706865775012560*erfi( 0.70710678118654752440*tm )*std::exp(-0.5*tm*tm) +
           0.59747883095511381408*std::exp(-0.5*tm*tm) + 1.2*exp(-0.5*t*t + t);
}