Math & Science ⇒ Equation Alignment Problems

[Jeremyrolph]

Hi guys,

I've just started using LaTeX and I'm having troubles using align. I am using the following piece of code:

Code: Select all

\begin{align*}
\begin{pmatrix}
\hat{S}^* \\
\hat{I}^*
\end{pmatrix}
=
\begin{pmatrix}
0 \\
0
\end{pmatrix}
\implies 
\lambda_{1}=u, \lambda_{2}=-v
\implies 
\begin{pmatrix}
0 \\
0
\end{pmatrix}
\textrm{is a stable node iff } u<0, v>0\\
\begin{pmatrix}
\hat{S}^* \\
\hat{I}^*
\end{pmatrix}
=
\begin{pmatrix}
1 \\
0
\end{pmatrix}
\implies 
\lambda_{1}=-u, \lambda_{2}=1-v
\implies 
\begin{pmatrix}
1 \\
0
\end{pmatrix}
\textrm{is a stable node iff } u>0, v>1\\
\begin{pmatrix}
\hat{S}^* \\
\hat{I}^*
\end{pmatrix}
=
\begin{pmatrix}
v \\
1-v
\end{pmatrix}
\implies 
P(\lambda)=\lambda^2 + (uv)\lambda + (uv-uv^2) 
\implies 
\begin{pmatrix}
v \\
1-v
\end{pmatrix}
\textrm{is a stable node iff } 0>uv, 0<v<1
\end{align*}

But this aligns totally incorrectly. Ideally I want to align the left hand sides (so the three (S*, I*) vectors are aligned below each other) and also drop the last \implies sign in the third equation to the line below (to make it fit on one page).

Can anyone help?

Thanks
Jezzer

[Boersma]

Well, this is quite a basic-question. Therefore, I recommend you to read the manual of amsmath. Chapter 3 gives a nice overview of all posibilities about alignments...

and, as Thorsten always says: Best regards, and welcome to the board.
Boersma

P.S. An MWE also contains a complete header, so if you add in your case

Code: Select all

\documentclass{minimal}
\usepackage{amsmath}

\begin{document}
.
.
\end{document} 

to your example, then everybody is happy.

[localghost]

Such alignments can sometimes be quite tricky. If I understand you right, the below example should do what you want.

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}   % loads »amsmath«

\begin{document}
  \begin{alignat*}{3}
    &&
    \begin{pmatrix}
      \hat{S}^* \\
      \hat{I}^*
    \end{pmatrix}
    &=
    \begin{pmatrix}
      0 \\
      0
    \end{pmatrix}\\
    &\implies &
    \lambda_{1}&=u &,\qquad \lambda_{2}&=-v \\
     &\implies&
     \begin{pmatrix}
       0 \\
       0
     \end{pmatrix}
     &\mathrlap{\text{ is a stable node if } u<0, v>0}\\[3\jot]
    &&
    \begin{pmatrix}
      \hat{S}^* \\
      \hat{I}^*
    \end{pmatrix}
    &=
    \begin{pmatrix}
      1 \\
      0
    \end{pmatrix} \\
    &\implies &
    \lambda_{1}&=-u  &,\qquad \lambda_{2}&=1-v \\
    &\implies &
    \begin{pmatrix}
      1 \\
      0
    \end{pmatrix}
    &\mathrlap{\text{ is a stable node if } u>0, v>1}\\[3\jot]
    &&
    \begin{pmatrix}
      \hat{S}^* \\
      \hat{I}^*
    \end{pmatrix}
    &=
    \begin{pmatrix}
    v \\
    1-v
    \end{pmatrix} \\
    &\implies &
    P(\lambda)&=\mathrlap{\lambda^2 + (uv)\lambda + (uv-uv^2)}\\
    &\implies &
    \begin{pmatrix}
    v \\
    1-v
    \end{pmatrix}
    &\mathrlap{\text{ is a stable node iff } 0>uv, 0<v<1}
  \end{alignat*}
\end{document}

I suggest to take a look at the respective manuals of the involved packages. Much useful tips regarding math typesetting can be found in the excellent »Math mode«.

Next time please provide a proper minimal example to give an adequate problem description. It's much better than some loose code snippets to test possible solutions.


Best regards and welcome to the board
Thorsten