fix mixture rule

Author: Hyeoksu Lee

src/simulation/m_bubbles_EE.fpp

@@ -242,16 +242,22 @@ contains
                             myalpha(ii) = q_cons_vf(advxb + ii - 1)%sf(j, k, l)
                         end do
 
-                        myRho = 0._wp
-                        n_tait = 0._wp
-                        B_tait = 0._wp
-
-                        $:GPU_LOOP(parallelism='[seq]')
-                        do ii = 1, num_fluids
-                            myRho = myRho + myalpha_rho(ii)
-                            n_tait = n_tait + myalpha(ii)*gammas(ii)
-                            B_tait = B_tait + myalpha(ii)*pi_infs(ii)/pi_fac
-                        end do
+                        if (num_fluids == 1) then
+                            myRho = myalpha_rho(1)
+                            n_tait = gammas(1)
+                            B_tait = pi_infs(1)/pi_fac
+                        else
+                            myRho = 0._wp
+                            n_tait = 0._wp
+                            B_tait = 0._wp
+
+                            $:GPU_LOOP(parallelism='[seq]')
+                            do ii = 1, num_fluids
+                                myRho = myRho + myalpha_rho(ii)
+                                n_tait = n_tait + myalpha(ii)*gammas(ii)
+                                B_tait = B_tait + myalpha(ii)*pi_infs(ii)/pi_fac
+                            end do
+                        end if
 
                         n_tait = 1._wp/n_tait + 1._wp !make this the usual little 'gamma'
                         B_tait = B_tait*(n_tait - 1)/n_tait ! make this the usual pi_inf