[Tex/LaTex] tikz: smooth curve and arrows

tikz-arrows

I am trying to draw a smooth curve in tikz that has an arrow tip both at the "beginning" and at the "ending".
It works fine when I add an arrow tip at the ending only (black curve below). However, when also specifying an arrow tip at the beginning the shape of the curve changes considerably and looks bumpy (red curve below):

How can I add the arrow tip at both sides and still have the shape of the black curve?

The code which I have used so far is:

\documentclass{standalone}

\usepackage{pgfplots}
\usetikzlibrary{arrows,arrows.meta}

\begin{document}

\begin{tikzpicture}

\begin{scope}[
    every node/.style = {
        draw            = green,
        fill            = green,
        inner sep       = 0pt,
        circle,
        minimum size    = 2pt,
        font            = \footnotesize,
}]

\node   (A1)    at (30:3.00cm){};
\node   (A2)    at (35:9.00cm){};
\node   (A3)    at (125:4.00cm){};

\end{scope}

\draw[thick,black] plot [smooth,tension=1] coordinates {(A1) (A2) (A3)};
\draw[-Latex,thick,black] plot [smooth,tension=1] coordinates {(A1) (A2) (A3)};
\draw[Latex-Latex,thick,red,dashed] plot [smooth,tension=1] coordinates {(A1) (A2) (A3)};

\end{tikzpicture}

\end{document}

Best Answer

You need to load the bending library:

\documentclass{standalone}

\usepackage{pgfplots}
\usetikzlibrary{arrows,arrows.meta,bending} %new code

\begin{document}

\begin{tikzpicture}

\begin{scope}[
    every node/.style = {
        draw            = green,
        fill            = green,
        inner sep       = 0pt,
        circle,
        minimum size    = 2pt,
        font            = \footnotesize,
}]

\node   (A1)    at (30:3.00cm){};
\node   (A2)    at (35:9.00cm){};
\node   (A3)    at (125:4.00cm){};

\end{scope}

\draw[thick,black] plot [smooth,tension=1] coordinates {(A1) (A2) (A3)};
\draw[-Latex,thick,black] plot [smooth,tension=1] coordinates {(A1) (A2) (A3)};
\draw[Latex-Latex,thick,red,dashed] plot [smooth,tension=1] coordinates {(A1) (A2) (A3)};

\end{tikzpicture}

\end{document}

Then it works.

Related Solutions

[Tex/LaTex] arrow heads in TikZ scaling and ending strangely

This is an interesting question. I could not understand properly how the keys length and width work but I noticed that using the option angle=<angle>:<dimension><line width factor> you may obtain the result you want and it also answers all of your questions.

I copy the definition of the above's option from the TikZ documentation:

This key sets the length and the width of an arrow tip at the same time. 
The length will be the cosine of <angle>, while the width will be twice
the sine of half the <angle>

I've assigned the valued angle=45:5pt 2 to all the arrows based on your question 3 (i.e. scaling according to the line width, in this case by a factor "2", by default it is 4.5). You can adjust those values as you wish:

\documentclass[tikz]{standalone}
\usetikzlibrary{calc,positioning,arrows.meta,quotes}
\begin{document}
    \begin{tikzpicture}[>={Latex[angle=45:5pt 2]}]
    \node[rectangle, draw=black, inner sep=.4cm](nCrystal) at (0,0) {Crys};
    \coordinate(pO) at ($(nCrystal.west)-(4,0)$);
    \coordinate(sO) at ($(nCrystal.west)-(2,1)$);
    \coordinate(pE) at ($(nCrystal.east)+(4,0)$);
    \coordinate(sE) at ($(nCrystal.east)+(2,1)$);
    \coordinate(iE) at ($(nCrystal.east)+(1.5,-0.92815)$);
    \coordinate[right=of nCrystal](cright);
    \draw [->,tips=proper,color=green,line width=2mm] (pO) edge["p"] (nCrystal.west);
    \draw [->,tips=proper,color=red, line width=.2mm] (sO) edge["s"] (nCrystal.west);
    \draw [->,tips=proper,color=green,line width=.5mm] (nCrystal.east) edge["p"] (pE);
    \draw [->,tips=proper,color=red,line width=1.7mm] (nCrystal.east) edge["s"] (sE);
    \draw [->,tips=proper,color=pink,line width=1.5mm] (nCrystal.east) edge["i"] (iE);
    \end{tikzpicture}
\end{document}

Just a quick note, tikz loads xcolor automatically so no need to add \usepackage{xcolor} in the preamble.

TikZ Arrows – TikZ Arrows of the Form =-> and -=>

Is this close to what you want?

\documentclass[tikz, border=5pt]{standalone}
\usetikzlibrary{decorations.pathreplacing, arrows}

\tikzset{
  -z>/.style={
    decoration={
      show path construction,
      lineto code={
        \path (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast) coordinate[pos=#1] (mid);
        \draw (\tikzinputsegmentfirst) -- (mid);
        \draw[double, -implies] (mid) -- (\tikzinputsegmentlast);      }
    },decorate
  }, -z>/.default=.5,
  z->/.style={
    decoration={
      show path construction,
      lineto code={
          \path (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast) coordinate[pos=#1] (mid);
                \draw[double] (\tikzinputsegmentfirst) -- (mid);
                \draw[->] (mid) -- (\tikzinputsegmentlast);
      }
    },decorate
  }, z->/.default=.5,
}

\begin{document}
\begin{tikzpicture}
  \draw [-z>] (0,0) -- (1,0);
  \begin{scope}[red, thick]
    \draw [z->=.3] (0,-.2) -- (1,-.4);
  \end{scope}
\end{tikzpicture}
\end{document}

I don't think you can have = as part of a style name, so I've denoted a double line with z. Note that the arrowheads aren't quite the same for the two styles, although this can probably be fixed. For some reason, styles directly on the \draw commands don't get reliably passed to the decorations, but if you need to style it further you can use a scope.

Best Answer

Related Solutions

[Tex/LaTex] arrow heads in TikZ scaling and ending strangely

TikZ Arrows – TikZ Arrows of the Form =-> and -=>

Related Question