How to connect two parabolic paths in TikZ?
Two separate lines canot be joined. You need to draw both parabolas in single path. Try:
\documentclass[12pt, tikz, border=0mm]{standalone}
\usetikzlibrary{arrows.meta, % <-- only this is needed
calc, intersections, through}
\newlength{\unit}
\tikzset{every label/.style = {label distance=2pt, inner sep=0pt},
every node/.style={font=\footnotesize},
> = {Stealth[width=4pt, length=5pt, inset=1pt]}
}
\begin{document}
\setlength{\unit}{0.5cm}
\begin{tikzpicture}[x=\unit, y=\unit, line width=2pt]
% Begin axes
\begin{scope}[line width=0.5pt]
\draw[->] (-3.5,0) -- (5.5,0);
\draw[->] (0,-0.1) -- (0,5.5);
\foreach \x in {-3, -2,...,5}
\draw (\x,2pt) -- ++ (0,-4pt) node[below] {$\x$};
\foreach \y in {1,...,5}
\draw (2pt,\y) -- ++ (-4pt,0) node[left] {$\y$};
\end{scope}% End axes
% the first parabola start at (5,0) and end at (3,5)
% wherends start the second, rotated one
% for this the bend of the first parabola is moved to the end of path
\draw (5,0) parabola[bend at end] (3,5) {[rotate around={-90:(3,5)}] parabola (5.5,-1)} ;
\end{tikzpicture}
\end{document}
Zarko's way is the most correct one, that's for sure. But, sometimes uniting the paths may be a ltttle tricky...
Then, there's a tricky way to make the paths look united, when in fact they are separate paths. To do this, one can use line cap
key which is originally set to butt
. In perpendicular joints is possible to use line cap=rect
which will make the paths look like they're sharply joined, or for all cases line cap=round
will make the paths look like they were roundly joined.*
Since the case here is a perpendicular join, it's possible to use rect
, but I've added more drawings to the MWE, just to show how line cap=round
always works but rect
not always. Also on the top left corner there's examples of all three line caps so that the difference is appreciated.
The full MWE:
\documentclass[12pt, tikz, border=2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{calc,intersections,through}
\tikzset{every label/.style = {label distance=2pt, inner sep=0pt}}
\tikzset{every node/.style={font=\footnotesize}}
\tikzset{> = {Stealth[width=4pt, length=5pt, inset=1pt]}}
\begin{document}
\newlength{\unit}
\setlength{\unit}{0.5cm}
\begin{tikzpicture}[x=\unit, y=\unit, line width=2pt]
% Begin axes
\begin{scope}[line width=0.5pt]
\draw[->] (-3.5,0) -- (5.5,0);
\draw[->] (0,-0.5) -- (0,5.5);
\foreach \x in {-3, -2, -1, 1, 2, 3, 4, 5}
\draw (\x,2pt) -- (\x,-2pt) node [anchor=base, shift={(0,-8pt)}, inner sep=1pt] {$\x$};
\foreach \y in {1, ..., 5}
\draw (2pt,\y) -- (-2pt,\y) node [anchor=east, inner sep=1pt] {$\y$};
\end{scope}
% End axes
\draw[line cap=rect] [rotate around={-90:(3,5)}](3,5) parabola (5.5,-1);
\draw (3,5) parabola (5,0);
%%MWE ends here -- the rest is for demonstration purposes only
\draw (1,0) -- (1,1);\draw[line cap=round] (1,1) -- +(135:1);
\draw (2,0) -- (2,1);\draw[line cap=rect] (2,1) -- +(135:1);
\draw (-3,5) -- +(1,0);\draw[ultra thin, white] (-3,5) -- +(1,0) node[font={\tiny\ttfamily},right,black]{butt};
\draw[line cap=round] (-3,4.5) -- +(1,0); \draw[ultra thin, white] (-3,4.5) -- +(1,0) node[font={\tiny\ttfamily},right,black]{round};
\draw[line cap=rect] (-3,4) -- +(1,0);\draw[ultra thin, white] (-3,4) -- +(1,0) node[font={\tiny\ttfamily},right,black]{rect};
\end{tikzpicture}
\end{document}
*Of course this is only valid for lines of the same width, if the lines have different widths they wont be joined properly with this method...