yt[1]=CubicSpline.interpolate(temperature, temp, rfInRe2, derivRe2);
yt[2]=CubicSpline.interpolate(temperature, temp, rfInRe3, derivRe3);
// cubic spline interpolation with respect to wavelength
CubicSpline cs = new CubicSpline(wavl, yt);
cs.calcDeriv();
yRe = cs.interpolate(wavelength);
return yRe;
}