add ZImage function for periodical boundary.

        return;

}

void ZImage(real8 boundMin[3], real8 boundMax[3], real8 *x, real8 *y, real8 *z)

{

        real8   xc, yc, zc;

        real8   invLx, invLy, invLz, Lx, Ly, Lz;

        xc = (boundMin[0] + boundMax[0]) * 0.5;

        yc = (boundMin[1] + boundMax[1]) * 0.5;

        zc = (boundMin[2] + boundMax[2]) * 0.5;

        Lx = boundMax[0] - boundMin[0];

        invLx = 1.0/Lx;

        Ly = boundMax[1] - boundMin[1];

        invLy = 1.0/Ly;

        Lz = boundMax[2] - boundMin[2];

        invLz = 1.0/Lz;

/*

 *      If periodic boundaries are not in use, the provided position

 *      of (x,y,z) will not be adjusted since there are no other

 *      images available.

 */

        *x -= rint(*x * invLx) * Lx;

        *y -= rint(*y * invLy) * Ly;

        *z -= rint(*z * invLz) * Lz;

        return;

}

real8 LinearInterpolation(const Curve_t &curve, real8 x, real8 min, real8 max)

{