docs: def _update_B(self):
          """Update `B`."""
          for param in self.freeparams:
              if param == 'mu':
                  continue
              paramval = getattr(self, param)
              assert isinstance(paramval, float), "Paramvalues must be floats"
              self.B[param] = broadcastMatrixMultiply(self.Ainv,
                      broadcastMatrixMultiply(self.dPxy[param], self.A))