# Multi-line equation alignment

I want to use multi-line equation in my essay but when I use it the alignment of the equations become destruct. please help me, thank you in advance

this is my code:

\documentclass[5p,fleqn]{elsarticle}

\usepackage{lineno,hyperref}
\modulolinenumbers[10]
\usepackage{amsmath}

\begin{document}

\begin{aligned} z=0, \forall r \in [R_i,R_o]: (uC_i)=(uC_i)_{in}, T=T_{in}, \\ P=P_{in}, (u_p C_{j,p})=0, \\ i=CH_4,H_2O, CO, CO_2, j=H_2O,H_2 \label{E21} \end{aligned}

$$\begin{split} r=r_0, \forall z \in [0,L]: \frac{\partial (uC_i)}{\partial r}=0,\\ k_a \frac{\partial T}{\partial r}=h_w (T_w-T) \label{E22} \end{split}$$

$$\begin{split} r=r_i, \forall z \in [0,L]: \frac{\partial (uC_i)}{\partial r}=0,\\ i=CH_4,H_2O, CO, CO_2,\\ \frac{d_p}{Pe_m}\frac{\partial (uC_j)}{\partial r}=N_m, j=H_2,\\ \frac{\partial T}{\partial r}=0 \label{E23} \end{split}$$

\end{document}


the result attached,

• Crosspost – Johannes_B Nov 22 '18 at 8:28
• It is still unclear to me what you are trying to align where. – Johannes_B Nov 22 '18 at 8:31
• I wanna to design my formula start from left edge of my essay and continue to right, I apologize in advance because I'm a beginner in latex – Alireza Abedin Nov 22 '18 at 8:36
• The description "I wanna design my formula [to] start from left edge of my essay and continue to right" is rather uninformative and nonspecific. Please be a lot more specific. – Mico Nov 22 '18 at 9:42

## 1 Answer

Welcome to TeX.SX!. I have the same opinion with @Mico, that you should explain what you want more, or at least we need a picture stating what you need, so that we don't have to guess :)

Anyway, I think this is what you need:

\documentclass{article}
\usepackage{amsmath}
\usepackage{lipsum}
\begin{document}
\lipsum[1]
\begin{align}
&\begin{array}{l}
z=0, \forall r \in [R_i,R_o]: (uC_i)=(uC_i)_{in},    T=T_{in},\\
P=P_{in}, (u_p C_{j,p})=0,\\
i=CH_4,H_2O, CO, CO_2,  j=H_2O,H_2
\end{array}\label{something1}\\[2ex]
&\begin{array}{l}
r=r_0, \forall z \in [0,L]: \dfrac{\partial (uC_i)}{\partial r}=0,\\
k_a \dfrac{\partial T}{\partial r}=h_w (T_w-T)
\end{array}\label{something2}\\[2ex]
&\begin{array}{l}
r=r_i, \forall z \in [0,L]: \dfrac{\partial (uC_i)}{\partial r}=0,\\
i=CH_4,H_2O, CO, CO_2,\\
\dfrac{d_p}{Pe_m}\dfrac{\partial (uC_j)}{\partial r}=N_m, j=H_2,\\[2ex]
\dfrac{\partial T}{\partial r}=0
\end{array}\label{something3}
\end{align}
\lipsum[2]
\end{document}


As for the chemical symbols like H2O, CO2..., I recommend using a package which is designed for chemistry. See other TeX.SX questions relating to this, for instance, How to write a chemical formula?, etc. I'm sorry not to use it in the code above, because I have never used it :)

• Thank you very much dear, You exactly do what I want. Thanks :) – Alireza Abedin Nov 22 '18 at 13:14