How to align negative and positive values inside an align environment?

Question

I have the following equation inside an align and split environment but I would like to align the values of the constants below (of c_1, c_2 and c_3) even with the negative sign.

\begin{align}
\begin{split} 
    \cos(x) &= c_1 + c_2x^2 + c_3x^4 \\
            &= c_1 + x^2(c_2 + c_3x^2) \\
    \text{where} \\
    c_1 &= 0.99940307 \\
    c_2 &= -0.49558072 \\
    c_3 &= 0.03679168 
\end{split}
\end{align}

This code generates this:

I wanted to align all values after the minus sign, like this:

How can I do this?

Note, however, that you are misusing both the align and the split environments, and that \text{where} should probably be \intertext{where}. I advise you to have a look at the manual of the amsmath package: on a TeXLive installation, it can be brought up by typing texdoc amsmath at a shell prompt. — GuM, Sep 26 '18 at 22:28
You could create break your column in two so that you can align on the decimal point. — A.Ellett, Sep 26 '18 at 23:01
@GuM: \shortintertext{where} might be better with the mathtools package. — Peter Grill, Sep 26 '18 at 23:08
@PeterGrill: I actually knew that, but I didn’t want to intimidate a (presumed) beginner with such niceties… ;-) — GuM, Sep 26 '18 at 23:15

score 2 · Answer 1 · answered Sep 27 '18 at 08:51

The simplest approach is to use a phantom where a sign is missing; \mathbin{\phantom{-}} will behave exactly like - in all situations, as far as spacing is concerned, but printing nothing.

\documentclass{article}
\usepackage{amsmath}

% first strategy
\newcommand{\nm}{\mathbin{\phantom{-}}}

% second strategy
\begingroup\lccode`~=``\lowercase{\endgroup\def~}{\mathbin{\phantom{-}}}
\AtBeginDocument{\mathcode``="8000 }

\begin{document}

\begin{equation}
\begin{split} 
    \cos(x) &= c_1 + c_2x^2 + c_3x^4 \\
            &= c_1 + x^2(c_2 + c_3x^2) \\
    \text{where} \\
    c_1 &= \nm 0.99940307 \\
    c_2 &=   - 0.49558072 \\
    c_3 &= \nm 0.03679168 
\end{split}
\end{equation}

\begin{equation}
\begin{split} 
    \cos(x) &= c_1 + c_2x^2 + c_3x^4 \\
            &= c_1 + x^2(c_2 + c_3x^2) \\
    \text{where} \\
    c_1 &= `0.99940307 \\
    c_2 &= -0.49558072 \\
    c_3 &= `0.03679168 
\end{split}
\end{equation}

\end{document}

The first strategy is simpler from a programming point of view; for the second I used a character that's not commonly used in math and made it “math active” expanding to the same phantom as in \nm.

score 0 · Answer 2 · answered Sep 27 '18 at 08:38

0

Following the approach provided in this answer

\documentclass{article}
\usepackage{mathtools}
\newlength{\myindent}
\setlength{\myindent}{10pt}
\newcommand{\LHS}[2][\myindent]{\hspace{#1}\mathrlap{#2}} 
\newcommand{\RHS}[2][\myindent]{\mathrlap{#2}\hspace{#1}}

\begin{document}
    \begin{align}
        \begin{split} 
            \cos(x) &= c_1 + c_2x^2 + c_3x^4 \\
            &= c_1 + x^2(c_2 + c_3x^2) \\
            \shortintertext{where}
            c_1 &= \LHS{0.99940307}\\
            c_2 &=\RHS{-}0.49558072\\
            c_3 &= \LHS{0.03679168}
        \end{split}
    \end{align}
\end{document}

answered Sep 27 '18 at 08:38

Diaa

9,599

The spacing is, however, off. The - on the r.h.s. is a unary operator. Add a line c_2 &= -0.49... to see what I mean. – campa Sep 27 '18 at 08:41
@campa I am sorry I couldn't understand what you mean. If you are talking about the spacing between - and 0.49..., it can be controlled by setting the length \myindent. – Diaa Sep 27 '18 at 08:45

How to align negative and positive values inside an align environment?

2 Answers2