How to graph piece wise function. f(x)={-x for -l

Question

f(x)={-x for -l<x≤0
          & 0 otherwise}

How to graph the above equation. pls help. also explain

I was unable to update my ques as it waa showing error so i jus use randim words and posted it. & I wanna know how to graph my function — Rahil gupta, Jan 03 '16 at 14:32
Rather than closing as unclear I would suggest flagging as low quality to have it deleted. — Henri Menke, Jan 03 '16 at 14:33
I simply want an answer on how to plot above function,thats it.! — Rahil gupta, Jan 03 '16 at 14:34
I see the problem with your post. It's allowed to use some HTML in questions, and HTML tags start with <. I guess the <x was interpreted as the start of a tag, but as it wasn't completed, it was discarded. Marking as code (select and hit Ctrl + K) helped things. — Torbjørn T., Jan 03 '16 at 14:42
@Rahilgupta Please help us to help you. Did you have a look at http://tex.stackexchange.com/search?q=plot+piecewise for already existing examples? What have you already tried? — samcarter_is_at_topanswers.xyz, Jan 03 '16 at 14:44
@Rahilgupta How about http://tex.stackexchange.com/a/261534/36296, this plots a function with 3 cases. — samcarter_is_at_topanswers.xyz, Jan 03 '16 at 14:49
Well am a new user here. How this site works,mean how generally 1 ask a question about. — Rahil gupta, Jan 03 '16 at 14:54
Hi and welcome to TeX.SX. In its current form, your question might not receive many answers. Please take a look at the How to Ask-page and try to improve your question according to the guidance found there. This may require you to show some effort on your part in terms of attempting a solution. If you have questions about what to do or if you don't quite understand what this means, please ask for clarification using the add comment function. — Martin Schröder, Jan 03 '16 at 15:19
This should not be closed yet. Please wait at least 24 hours after asking the OP for improvements to the question before voting to close. Also, if you downvote, please don't forget to revert the vote after the question is improved. — Martin Schröder, Jan 03 '16 at 15:20
@Rahilgupta You have by now received 7 high-quality answers to your poorly phrased question. Please mark one of them as ‘Accepted’ by clicking on the tickmark below their vote count (see How do you accept an answer?). This shows which answer helped you most, and it assigns reputation points to the author of the answer (and to you!). It's part of this site's idea to identify good questions and answers through upvotes and acceptance of answers. — Henri Menke, Feb 22 '16 at 14:39

score 14 · Answer 1 · edited Apr 13 '17 at 12:35

I suggest you use the pgfplots package. Since your function has three intervals I split the plot in these three

 0  for x ≤ -l
-x  for -l < x ≤ 0
 0  for 0 < x

There is a discontinuity point at x = -l, so I drew a filled circle at f(-l) = 0 and an empty circle at f(-l) = l.

Also, don't forget to jksabn a alkew klakjlre.

\documentclass{article}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    xlabel={$x$},ylabel={$f(x)$},
    xtick={-1,0},xticklabels={$-l$,$0$},
    ytick={0,1},yticklabels={$0$,$l$},
    no marks,
    ]
    \addplot[blue,domain=-2:-1] {0};
    \addplot[blue,domain=-1:0] {-x};
    \addplot[blue,domain=0:2] {0};
    \node[blue,draw,fill=blue ,circle,inner sep=1pt] at (axis cs:-1,0) {};
    \node[blue,draw,fill=white,circle,inner sep=1pt] at (axis cs:-1,1) {};
  \end{axis}
\end{tikzpicture}
\end{document}

Zarko · Answer 2 · 2016-01-03T15:07:36.973

9

Probably you like to draw single saw tooth ...

With help of TikZ it is easy:

\documentclass[border=3mm,tikz]{standalone}

\begin{document}
\begin{tikzpicture}
\draw[ ->]  (0,-0.1) node[below] {0} -- (0,2) node[below right] {$f(x)$};
\draw[<->]  (-3,0) node[below] {$-\infty\gets x$} -- 
            ( 3,0) node[below] {$x \to +\infty$};
\draw   (-0.1,1) node[left] {1} -- + (0.2,0);
\draw   (-1,0.1) -- + (0,-0.2) node[below] {$-1$};
%
\draw[very thick,red]   (-2.5,0) -- (-1,0)
                        (-1.0,1) -- (0,0)
                        ( 0.0,0) -- (2.5,0);
\draw[very thin,dashed,red] (-1,0) -- (-1,1);
\end{tikzpicture}            
\end{document}

edited Jan 03 '16 at 15:07

answered Jan 03 '16 at 14:57

Zarko

296,517

1

There is a handy synonym for \leftarrow which is \gets (just as \to for \rightarrow) – Henri Menke Jan 03 '16 at 15:04
Thank for editing my answer, it seems that new year is to young that I will be full operational :( , – Zarko Jan 03 '16 at 15:05
@HenriMenke, thank you for \gets, I will consider it. – Zarko Jan 03 '16 at 15:06

score 7 · Answer 3 · answered Jan 03 '16 at 18:40

7

For the sake of quackiness, let us add a gnuplot hybrid solution! :)

% arara: pdflatex: { shell: yes }
\documentclass{article}

\usepackage{gnuplottex}

\begin{document}

\begin{gnuplot}[terminal=pdf]
set key inside left top vertical Right noreverse enhanced autotitles box linetype -1 linewidth 1.000
f(x) = -1 < x && x <= 0 ? -x : 0
plot f(x)
\end{gnuplot}

\end{document}

The output:

answered Jan 03 '16 at 18:40

Paulo Cereda

44,220

Something's weird with gnuplot's choice of points for this plot: the line never gets to (-1, 1) or (0, 0). – Mike Renfro Jan 04 '16 at 04:30
@Mike: indeed, I will take a look later, I believe it's a matter of specifying the desired range. I don't even use gnuplot that much. :) – Paulo Cereda Jan 04 '16 at 08:09
@PauloCereda Might also be related to the amount of sampled points, I'd guess. If yes, 'set sample 1000' should help. And why using the pdfterminal if there is the cairolatex or even tikz terminal? :p – John Mar 21 '16 at 16:16

Bernard · Answer 4 · 2016-01-03T15:56:43.113

Here is a way with pstricks:

\documentclass[border=4pt, svgnames]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\usepackage{pst-plot, pst-node}
\usepackage{auto-pst-pdf}

\begin{document}

\psset{unit=3cm, arrowinset=0.12, ticksize= -2pt 2pt, linejoin=1}
\begin{pspicture*}(-2.6,-1.1)(1.6,1.9)
    \psaxes[linecolor=LightSteelBlue, tickcolor=LightSteelBlue]{->}(0,0)(-2.6,-1.1)(1.6,1.9)[$x$, -135] [$y$,-135]%
    \uput[dl](0,0){0}
    \pnode(-2.6,0){A}\pnode{} \pnode(0,0.9pt){O} \pnode(1.55,0.9pt){B}\pnode(-1,0){C}\pnode(-1,1){D}
    \psline[linestyle=dashed, dash=4pt 4pt, linewidth=0.3pt](0,1)(D)(C)
    \psset{linecolor=IndianRed}
    {\psset{linewidth =1.2pt}
    \ncline[offset=0.9pt, dotsize=3pt, arrows=-*]{A}{C}\psline(D)(O)(B)}
    \psdot[dotstyle=o](D)
\end{pspicture*}

\end{document}

score 2 · Answer 5 · answered Jan 05 '16 at 11:02

Another way with mfpic, a very efficient LaTeX interface to MetaPost:

\documentclass[border=2mm]{standalone}
\usepackage[metapost]{mfpic}
\setlength{\mfpicunit}{1cm}
\opengraphsfile{\jobname}
\begin{document}
\begin{mfpic}[3]{-2.5}{1.5}{-0.5}{1.5}
   \doaxes{xy}
   \dashed\lines{(-1, 1), (0, 1)}
   \drawcolor{red}
   \dashed\lines{(-1, 0), (-1, 1)}
   \penwd{1bp}
   \lines{(\xmin, 0), (-1, 0)}
   \lines{(-1, 1), (0, 0), (\xmax-.04, 0)}
   \pointcolor{red}
   \point[4pt]{(-1, 0)}
   \pointfillfalse
   \point[4pt]{(-1, 1)}
   \tlpointsep{3bp}
   \tlabels{[tc](\xmax, 0){$x$} [cr](0, \ymax){$y$} [tr](0, 0){$O$}
     [tc](-1, 0){$-1$} [br](0, 1){$1$}}
\end{mfpic}
\closegraphsfile
\end{document}

To be compiled with LaTeX, then MetaPost, then LaTeX again. Result:

score 2 · Answer 6 · answered Jan 05 '16 at 18:09

With Asymptote.

settings.outformat="pdf";
import graph;

size(6cm,4cm,IgnoreAspect);

real l = 1;
real epsilon = 1e-16;

real f(real x) {
  if (-l < x && x <= 0)
    return -x;
  else
    return 0;
}

draw(graph(f, -2, -l-epsilon),blue);
draw(graph(f, -l+epsilon, 2),blue);
dot((-l,f(-l-epsilon)),blue);
dot((-l,f(-l+epsilon)),blue,UnFill);

ylimits(-0.2,1.2);

xaxis("$x$",BottomTop,LeftTicks);
yaxis("$y$",LeftRight,RightTicks);

score 2 · Answer 7 · answered Jan 05 '16 at 23:30

2

A solution using R, embedded in the LaTeX source file, precompiled using knitr.

\documentclass[border=.25in]{standalone}
\begin{document}
<<echo=FALSE>>=
plot(NA,xlim=c(-2,2),ylim=c(-.2,1.2),xlab="x",ylab="y") 
curve(0*x, from=-2, to=-1, add=TRUE)
curve(-x, from=-1, to=0, add=TRUE)
curve(0*x, from=0, to=2, add=TRUE)
@
\end{document}

answered Jan 05 '16 at 23:30

R. Schumacher

9,895

0*x is quite impressive. I would suggest using lines(c(-2,-1), rep(0,2)) etc., points with pch=16 to show inclusion/exclusion, and finally, set the ylim=c(-0.05, 1.05). And probably asp=1, too. – Andreï V. Kostyrka Jan 24 '16 at 16:13

How to graph piece wise function. f(x)={-x for -l

7 Answers7