[Tex/LaTex] Tikz-cd and snake lemma: “loseness” and centered figures

tikz-cdtikz-pgf

I have to draw a snake lemma, as here: snake lemma.

The code is

\documentclass{article}
    \usepackage{tikz-cd}
    \usepackage{amsmath}
    \DeclareMathOperator{\Tor}{Tor}
    \begin{document}
    \begin{tikzcd}
              \cdots \rar   & \Tor_3^A(A, M) \rar & \Tor_3^A(K,M) \rar & \Tor_3^A(K/A,M) \ar[out=0, in=180, looseness=2]{dll}   & \\
                    & \Tor_2^A(A, M) \rar & \Tor_2^A(K,M) \rar & \Tor_2^A(K/A,M) \ar[out=0, in=180, looseness=2]{dll}   & \\
                    & \Tor_1^A(A, M) \rar & \Tor_1^A(K,M) \rar & \Tor_1^A(K/A,M) \ar[out=0, in=180, looseness=2]{dll}   & \\
                    & A \otimes_A M  \rar & K \otimes_A M \rar & K/A\otimes_A M \rar                    & 0
        \end{tikzcd}
\end{document}

The resulting diagram is shifted on the very right side of the page. The more I increase the value of looseness the more the figure is shifted.

How can I center the figure?

Best Answer

You can add the overlay option to those problematic arrows, so they don't affect the bounding box calculation. I did it in this MWE, now the diagram is centered:

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amsmath}
\DeclareMathOperator{\Tor}{Tor}
\begin{document}
\begin{tikzcd}
  \cdots \rar   & \Tor_3^A(A, M) \rar & \Tor_3^A(K,M) \rar & \Tor_3^A(K/A,M)
          \ar[out=0, in=180, looseness=2, overlay]{dll}   & \\
        & \Tor_2^A(A, M) \rar & \Tor_2^A(K,M) \rar & \Tor_2^A(K/A,M)
          \ar[out=0, in=180, looseness=2, overlay]{dll}   & \\
        & \Tor_1^A(A, M) \rar & \Tor_1^A(K,M) \rar & \Tor_1^A(K/A,M)
          \ar[out=0, in=180, looseness=2, overlay]{dll}   & \\
        & A \otimes_A M  \rar & K \otimes_A M \rar & K/A\otimes_A M \rar & 0
\end{tikzcd}
\end{document}

centered diagram

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[Tex/LaTex] How to put a coloured outline around fraction lines

Knuth in the TeXBook gave an example of "poor man's bold," (The TeXbook, p. 386) which can be typeset obtained by overprinting the normal weight symbol with slight offsets.

As he says:

The results are somewhat fuzzy, and they certainly are no match for the real thing if it's available; but poor man's bold is better than nothing, and once in a while you can get away with it.

Here, one can use a similar technique and the code is shown below:

\documentclass{article}
\usepackage{graphicx,xcolor} 
\usepackage{amsmath}
\def\PoorManContour#1#2#3{\leavevmode
    \setbox0=\hbox{{#1}}%
    \color{#3}\kern-.002em\copy0\kern-\wd0
    \color{#3}\raise-.04em\copy0\kern-\wd0
    \color{#3}\lower.04em\copy0\kern-\wd0
    \color{#3}\raise0.04em\copy0\kern-\wd0
    \color{#2}\raise-.012em\copy0\kern-\wd0
    \color{#2}\kern.06em\copy0\kern-\wd0
    \color{blue}\kern-.020em\lower.003em\box0
}
\begin{document}
\colorbox{gray!5}{\scalebox{5}{\PoorManContour{$\sqrt{\dfrac{A^3_i}{B^2}}$}{gray!60}{gray!60}}}
\end{document}

To achieve the best results possible one has to kern in small steps for possibly twenty steps or so. For simplicity, I have not done that. In the final version, you need to adjust the colors to suit, possibly changing the shading to white.

alt text

Edit

After reading Jan's comment below I read the manual and true, as the commenter said the easiest way to achieve what the OP wanted is to include the package without an option i.e., \usepackage{contour}. Helps to RFM!

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

Best Answer

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