def METHOD_NAME(self, mat, nuc, rx, value):
    """Set reaction rate by material/nuclide/reaction
    Parameters
    ----------
    mat : str
        Material ID as a string
    nuc : str
        Nuclide name
    rx : str
        Name of the reaction
    value : float
        Corresponding reaction rate to set
    """
    mat = self.index_mat[mat]
    nuc = self.index_nuc[nuc]
    rx = self.index_rx[rx]
    self[mat, nuc, rx] = value