[pstricks] Re: area under a curve

[Denis Girou]

The following message is a courtesy copy of an article
that has been posted to comp.text.tex as well.

>>>>> "Gregory.Gibby" == Gregory Gibby <berton at et.byu.edu> writes:

    Gregory.Gibby> hello
    Gregory.Gibby> I am using pstricks to write test questions for basic calc.
    Gregory.Gibby> I am having trouble finding a command or technique that will
    Gregory.Gibby> shade or crosshatch the area between a curve and the x-axis.

    Gregory.Gibby> the type of curve is x^2 - 2*x (or x x mul x 2 mul sub for you
    Gregory.Gibby> rpn addicts) from 0 to 4, so the shading has to up from the
    Gregory.Gibby> parabola to the x-axis on one part and down from the parabola
    Gregory.Gibby> to the axis on another part.

    Gregory.Gibby> the documentation I have seen only lets you shade parabolas
    Gregory.Gibby> symmetrically.  like you were filling them with water.

    Gregory.Gibby> I'm sure that this is an easily solved problem, but I can't find a good
    Gregory.Gibby> answer on google or in the graphics companion or the PST doc's.

  See for instance paragraphs 19 and 20 (pages 35-37) of the User's guide,
paragraph 4.10 (pages 142-145) of the LaTeX Graphics Companion or the
http://tug.org/applications/PSTricks/Mathematics/
Web page for some more complex examples.

\documentclass{article}

\usepackage{pst-plot}

\pagestyle{empty}

\begin{document}

\begin{center}
  \begin{displaymath}
    f(x)=x^2 - 2x
  \end{displaymath}

  \begin{pspicture}(-0.5,-1.5)(4,8)
    \psaxes(0,0)(0,-1)(4,8)
    \pscustom[fillstyle=crosshatch]{%
      \psplot{0}{4}{x x mul x 2 mul sub}
      \psline(4,0)}
  \end{pspicture}
\end{center}

\end{document}

Denis Girou
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