def _compute_kernel(sigma, R):
    """
    Computes the kernel of a Gaussian Process.

    Parameters
    ----------
    sigma : float
        Standard deviation.
    R : array_like
        Matrix or vector of correlation coefficients.

    Returns
    -------
    C : array_like
        Kernel or Covariance Matrix of a Gaussian Process.
    """

    return sigma ** 2. * R