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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def opt_to_ri(f, res, nm):
 r"""Convert the OPT object function to refractive index In :abbr:`OPT (Optical Projection Tomography)`, the object function is computed from the raw phase data. This method converts phase data to refractive index data. .. math:: n(\mathbf{r}) = n_\mathrm{m} + \frac{f(\mathbf{r}) \cdot \lambda}{2 \pi} Parameters f: n-dimensional ndarray The reconstructed object function :math:`f(\mathbf{r})`. res: float The size of the vacuum wave length :math:`\lambda` in pixels. nm: float The refractive index of the medium :math:`n_\mathrm{m}` that surrounds the object in :math:`f(\mathbf{r})`. Returns ------- ri: n-dimensional ndarray The complex refractive index :math:`n(\mathbf{r})`. Notes ----- This function is not meant to be used with diffraction tomography data. For ODT, use :py:func:`odt_to_ri` instead. """

    ri = nm + f / (2 * np.pi) * res
    return ri