Math & Science ⇒ can't automatically align text in align environment

[Theo]

Hi I have succeeded to make the following equations nicely aligned but I had to do it manually by adding the \hspace commands to align the text. This took much too long to be worthwhile! There must be a way LaTeX can do this automatically.

Also I wanted to number each one of the three equations in my array environment but could not find the relevant help.

Please somebody?

My (halfbacked and time consuming solution - I also like to have these equations framed):

\begin{framed}
Summary of PPMA time-dependent trajectories
\begin{align}
x = x(t) = & \, x_i+{v_i}_x t \hspace{38mm} \text{(All regions)}\label{eqxt}\\
y = y(t) = & \left\{ \begin{array}{llll}
& \hspace{-5mm} \phantom{-}y_i+{v_i}_y t & (\text{region I: } t \leq t_2 = -y_i/{v_i}_y) \\
& \hspace{-5mm} \phantom{-}{v_i}_y (t-t_2) + \frac{1}{2} a (t-t_2)^2 & (\text{region II: } t_2 \leq t \leq t_3)\\
& \hspace{-5mm} -{v_i}_y(t-t_3) & (\text{region III: } t \geq t_3 = -y_i/{v_i}_y-2{v_i}_y/a )\\
\end{array}
\right.\label{eqyt}\\
z = z(t) = & \, z_i+{v_i}_z t \hspace{38mm} \text{(All regions)} & \label{eqzt}
\intertext{with}
a = & \, a_y = -(q/m) V_d/d < 0 \hspace{13mm} \text{(acceleration in II)} \label{eqa}\\
y(t_2) = & \, y(t_3) = 0 \hspace{36.5mm}\text{(ground plate of PPMA)} \label{eqyplate}
\end{align}
\end{framed}

[localghost]

I can offer at least a partial solution. Try another approach with the alignat environment and two arrays. I would not number all the lines in the arrays because these are just cases for the value of one function thus represent one equation. It could be confusing.

Code: Select all

\documentclass[10pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{geometry}
\usepackage{mathtools}

\begin{document}
  \begin{alignat}{3}
    x &= x(t) &&= x_i+{v_i}_x t &&\quad \text{(All regions)}\label{eqxt}\\
    y &= y(t) &&= \left\{
                    \begin{array}{@{}l@{}}
                      \phantom{\mathrel{-}}y_i+{v_i}_y t \\
                      \phantom{\mathrel{-}}{v_i}_y (t-t_2) + \frac{1}{2} a (t-t_2)^2 \\
                      -{v_i}_y(t-t_3) \\
                    \end{array}\right. &&\quad
                    \begin{array}{@{}l@{}}
                      (\text{region I: } t \leq t_2 = -y_i/{v_i}_y) \\
                      (\text{region II: } t_2 \leq t \leq t_3) \\
                      (\text{region III: } t \geq t_3 = -y_i/{v_i}_y-2{v_i}_y/a )\\
                    \end{array} \label{eqyt} \\
    z &= z(t) &&= z_i+{v_i}_z t &&\quad \text{(All regions)} \label{eqzt}
    \intertext{with}
    a &= a_y &&= -(q/m) V_d/d < 0 &&\quad \text{(acceleration in II)} \label{eqa}\\
    y(t_2) &=  y(t_3) &&= 0 &&\quad \text{(ground plate of PPMA)} \label{eqyplate}
  \end{alignat}
\end{document}

Finally some remarks.

• Please always check your examples for completeness and functionality. They must be compilable for others as provided.
• The forum software offers a »Code« tag for formatting code thus better recognition. It can be found among others in the button list right above the input window.

Best regards and welcome to the board
Thorsten