I am trying to make a graph of some floor/ceiling functions for examplep the floor of 3x+2 like this: http://www.wolframalpha.com/input/?i=graph+of+floor%283x%2B2%29#=.
However, I searched through the PFGPlots manual and did not find a mention of that. Does anyone know how to do this in LaTeX or PGFplots?
You can use the jump mark mid style for this, which draws horizontal unconnected line segments.
\begin{tikzpicture}
\begin{axis}[axis lines=middle]
\addplot [
jump mark mid,
domain=-3:3,
samples=100,
very thick, red
] {floor(3*x)+2};
\end{axis}
\end{tikzpicture}
to get
A fancier approach could be to use the discontinuous style from the question Probability density function of Uniform Distribution to plot the intervals.
ceil function isn't defined in PGFPlots by default, but you can easily define it yourself (I've edited my answer). Sorry about the connecting line, that was an oversight on my part. It's fixed now. The title=<text> code goes in the axis options, so you'd say \begin{axis}[title=My title, axis lines=middle].
– Jake
Jun 10 '13 at 04:03
\addplot [ domain=-3:3, samples=121, jump mark mid, discontinuous, very thick, blue ] {Floor(2*(Ceil(x/2))+.5)};
– Jake
Jun 10 '13 at 04:27
Floor(x) instead of Floor(3*x+2), the point at x=0 seems shifted to the right for some reason. The other discontinuities are fine, just the one at x=0 has an issue.
– Peter Grill
Jun 08 '15 at 07:54
ceil(1.0) should be 1.0, but round(1.0 + 0.5) is round(1.5) which is 2.0.
– wchargin
Sep 25 '16 at 00:56
ceil and floor functions have been added to the FPU library, so I've removed the wrong definition from my answer.
– Jake
Sep 25 '16 at 08:52
Two small refinements to Jake's solution:
The start and end line have only half of the line width as the
other lines because of pgfplot's clipping of the plot area.
This can be fixed by either disable clipping clip=false or
enlarging the plot are in the vertical directions: enlarge y limits={abs=.6pt} (very thick is 1.2pt).
The more serious issue is that the start and end points of the lines
are not correct, after adding option grid:
The sample points left and right of a jump value do not have the same distance, for example at x = 1.
There are two ways of fixing it:
The first way works by accident only:
\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\begin{document}
\begin{tikzpicture}
\begin{axis}[axis lines=middle, grid, clip=false]
\addplot [
jump mark right,
mark=*,
domain=-3:3,
samples=19,
very thick, red
] {floor(3*x)+2};
\end{axis}
\end{tikzpicture}
\end{document}
The sample points are marked. The number of samples is the number of lines plus one for an additional end point:
It works only, because x values for the sample points except the first are a tiny bit (rounding error) too small.
A more stable solution is to use the middle points of the lines. Unhappily it complicates the domain and plot area options. Version with grid and marked sample points and without clipping:
\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
axis lines=middle,
grid,
clip=false,
xmin=-3,
xmax=3,
ymin=-7,
ymax=10,
enlarge y limits={abs=.6pt}, % very thick: 1.2pt
]
\addplot [
jump mark mid,
mark=*,
domain=-3 - 1/6:3 + 1/6,
samples=20,
very thick, red
] {floor(3*x)+2};
\end{axis}
\end{tikzpicture}
\end{document}
And the final solution:
\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
axis lines=middle,
xmin=-3,
xmax=3,
ymin=-7,
ymax=10,
enlarge y limits={abs=.6pt}, % very thick: 1.2pt
]
\addplot [
jump mark mid,
domain=-3 - 1/6:3 + 1/6,
samples=20,
very thick, red
] {floor(3*x)+2};
\end{axis}
\end{tikzpicture}
\end{document}
ceiland afloorfunction. Thepgfplotsoffers a few options for Constant Plots (see manual v1.8, subsection 4.4.3, pp. 57ff.). The optionjump mark leftfor example might help. – Qrrbrbirlbel Jun 10 '13 at 03:18