calc_srtm_tac
=============================================================

.. py:function:: petpal.kinetic_modeling.reference_tissue_models.calc_srtm_tac(tac_times_in_minutes: numpy.ndarray, ref_tac_vals: numpy.ndarray, r1: float, k2: float, bp: float) -> numpy.ndarray

   Calculate the Time Activity Curve (TAC) using the Simplified Reference Tissue Model (SRTM)
   with the given reference TAC and kinetic parameters.

   .. important::
       This function assumes that the reference TAC is uniformly sampled with respect to time
       since we perform convolutions.


   The SRTM TAC can be calculated as:

   .. math::

       C(t)=R_{1}C_\mathrm{R}(t) + \left(k_{2} - \frac{R_{1}k_{2}}{1+\mathrm{BP}}\right)
       C_\mathrm{R}(t)\otimes\exp\left(- \frac{k_{2}t}{1+\mathrm{BP}}\right),


   where :math:`C_\mathrm{R}(t)` is the reference TAC, :math:`R_{1}=\frac{k_1^\prime}{k_1}`,
   :math:`k_{2}` is the rate-constant from the tissue compartment to plasma, and
   :math:`\mathrm{BP}` is the binding potential.


   :param tac_times_in_minutes: The array representing the time-points for both TACs.
   :type tac_times_in_minutes: np.ndarray
   :param r1: The ratio of the clearance rate of tracer from plasma to the reference to the
              transfer rate of the tracer from plasma to the tissue;
              :math:`R_{1}\equiv\frac{k_1^\prime}{k_1}`.
   :type r1: float
   :param k2: The rate constant for the transfer of the tracer from tissue compartment to
              plasma.
   :type k2: float
   :param bp: The binding potential of the tracer in the tissue.
   :type bp: float
   :param ref_tac_vals: The values of the reference TAC.
   :type ref_tac_vals: np.ndarray

   :returns: *np.ndarray* -- TAC values calculated using SRTM.

   :raises AssertionError: If the reference TAC and times are different dimensions.