Math & Science ⇒ align* not vertically aligned on left

[Singularity]

For my edification, why doesn't the align* environment in my code left justifying all of the equations the same? Look closely at the attached pic and you'll see that the align* example is not fully flush left on the two lines following the vertical dots (which are also the two lines using capital letters as subscripts).

I've tried adding double ampersands (&), like in the alignat* example. I tried adding ampersands at the beginning and end of the line, and combinations of double ampersands, beginning and end.

As you can see, I have this working adequately using alignat*. So this question is mostly for my LATEX education.

Thanks.

Code: Select all

\documentclass[12pt,fleqn,reqno]{article}
%fleqn: left align equations
%reqno: equation numbers on right
\usepackage{amsfonts,graphics,epsfig,cite}
\usepackage{amsmath,graphicx,amssymb,amsthm}
                                 
\begin{document}
\underline{\textbf{alignat*}}
\begin{alignat*}{2}
	&v_1				&&=\dot{u}_1 \\
	&v_2				&&=\dot{u}_2 \\
	&\vdots			&&						\\
	&v_N				&&=\dot{u}_N	\\
	&\dot{v}_1	&&=k(u_0-2u_1+u_2) \\
	&\dot{v}_2	&&=k(u_1-2u_2+u_3) \\
	&\vdots			&&									\\
	&\dot{v}_N	&&=k(u_{N-1}-2u_N+u_{N+1})
.\end{alignat*}

\underline{\textbf{align*}}
\begin{align*}
	v_1				&=\dot{u}_1 \\
	v_2				&=\dot{u}_2 \\
	\vdots			&						\\
	v_N				&=\dot{u}_N	\\
	\dot{v}_1	&=k(u_0-2u_1+u_2) \\
	\dot{v}_2	&=k(u_1-2u_2+u_3) \\
	\vdots			&									\\
	\dot{v}_N	&=k(u_{N-1}-2u_N+u_{N+1})
.\end{align*}
\end{document}

[Stefan Kottwitz]

Hi,

they are left aligned, however there's a predefined indentation. You can modify it by setting

Code: Select all

\setlength{\mathindent}{0pt}

Stefan

[Singularity]

Thanks. But I may not have worded my question correctly.

Using "\setlength{\mathindent}{0pt}" moved all of the equations in the entire document to have no indent.

What I really meant to ask is how come two of the lines have a small "outdent"? Notice in the attached that two lines hang out a small amount compared to the other six lines. The line which starts "v_N=..." (the 4th line) and the last line, which starts "v dot_N=..." seem to hang farther to the left than the other lines of the align statement. Why aren't they all vertically aligned?

And now, I think I have just figured out the answer (while typing this post): the align environment, as I've coded it, aligns each line by the equal sign. If v_N is wider than v_1 and v_2, then it will extend farther left from the equal sign than the other lines. align is working as designed, the author (that's me!) is not using it correctly.

Code: Select all

\documentclass[12pt,fleqn,reqno]{article}
%fleqn: left align equations
%reqno: equation numbers on right
\usepackage{amsfonts,graphics,epsfig,cite}
\usepackage{amsmath,graphicx,amssymb,amsthm}
                                 
\begin{document}
\underline{\textbf{align*}}
\begin{align*}
   v_1         &=\dot{u}_1       \\
   v_2         &=\dot{u}_2       \\
   \vdots      &                 \\
   v_N         &=\dot{u}_N       \\
   \dot{v}_1   &=k(u_0-2u_1+u_2) \\
   \dot{v}_2   &=k(u_1-2u_2+u_3) \\
   \vdots      &                 \\
   \dot{v}_N   &=k(u_{N-1}-2u_N+u_{N+1})
.\end{align*}
\end{document}

The fix to the problem is to use alignat:

Code: Select all

\begin{alignat}{2}
  &v_1		&&=\dot{u}_1 	   \notag \\
  &v_2		&&=\dot{u}_2 	   \notag \\
  &\vdots	&&		   \notag \\
  &v_{_N}	&&=\dot{u}_{_N}	   \notag \\
  &\dot{v}_1	&&=k(u_0-2u_1+u_2) \label{eq:firstorderFPU} \\
  &\dot{v}_2	&&=k(u_1-2u_2+u_3) \notag \\
  &\vdots	&&		   \notag \\
  &\dot{v}_{_N}	&&=k(u_{_{N-1}}-2u_{_N}+u_{_{N+1}}) \notag 
.\end{alignat}

P.S. I'm going to change the subject of this thread, if possible, to better reflect my actual question (and marking it solved).