I am writing an optimization problem for a scientific paper using IEEE tran conference library. I am splitting long equations into 2 lines but then, latex is putting equation number on both lines. Below is the MWE related to my problem. Eq 1b and 1c is just one equation; similarly 1d and 1e is just one equation. I want to write them in two lines but want equation number only one the second line.
\documentclass[conference]{IEEEtran}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\begin{subequations}
\begin{alignat}{2}
& (P1) \hspace{0.5em}\!\min_{\vartheta} &\qquad& f(\vartheta) \label{eq:OF}\\
&\text{subject to} & & V_i^\varphi I_i^{*\varphi} = (P_{g_i}^\varphi-P_{l_i}^\varphi)+j(Q_{g_i}^\varphi-Q_{l_i}^\varphi),\label{eq:PBG}\\
& & & \forall \varphi \in \phi_{i}, i \in G\\
& & & V_k^\varphi I_k^{*\varphi} = (-P_{l_k}^\varphi -jQ_{l_k}^\varphi)+jy_{c_k}^\varphi|V_k|^2,\label{eq:PBL}\\
& & & \forall \varphi \in \phi_{k}, k \in N\backslash \{G\}\\
& & & (\underline{V}_k)^2 \leq |V_k^\varphi|^2 \leq (\overline{V_k})^2, \forall \varphi \in \phi_{k}, k \in N,\label{eq:Vol}\\
& & & \underline{P}_{g_i} \leq P_{g_i}^\varphi \leq \overline{P}_{g_i}, \forall \varphi \in \phi_{i}, i \in G,\label{eq:GenP}\\
& & & \underline{Q}_{g_i} \leq Q_{g_i}^\varphi \leq \overline{Q}_{g_i}, \forall \varphi \in \phi_{i}, i \in G,\label{eq:GenQ}
\end{alignat}
\end{subequations}
\end{document}
\nonumber
before change the line.\hspace{0.5em}\!
. Replace by\
, for example.