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As the image shows I am drawing two curves y=x^3-8 and its inverse y=(x+8)^(1/3) using \tkzFct. As you can see the first graph plots fine suggesting that GnuPlot is working ok and set up properly in my system.

When I increase the domain for the second function the whole graph does not plot. The red bit is missing!

Unfortunately the manual is in French so I am struggling to access!

The image i am hoping to achieve

My MWE

\usepackage[left=8mm, top=12mm, right=10mm, bottom=12mm]{geometry}

\usepackage{pgfplots}
\usepackage{tkz-base}
\usepackage{tkz-fct}


\begin{document}
\begin{center}
    \begin{tikzpicture}[scale=0.6]
        \tkzInit[xmin=-20,xmax=4,ymin=-9,ymax=4]
        \tkzDrawX[line width=0.9mm]
        \tkzDrawY[line width=0.9mm]
        %\tkzGrid[color=gray!70,line width=0.05mm]
        %   \tkzLabelY[orig] \tkzLabelX[swap]
        \tkzFct[domain=-4:6,line width=0.5mm,samples=400]{x3-8}
        \tkzFct[domain=-12:4,line width=0.5mm,samples=400]{(x+8)(0.33333)}
    \end{tikzpicture}
\end{center}
\end{document} ```
ToyBoy
  • 117

1 Answers1

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It appears that Gnu Plot does not like cube rooting negative numbers. By using the sign of the x term and the absolute cube root of x and then combining along with thought out domains it works.

This is the code I added!!

\tkzFct[domain=-10:-8,line width=0.5mm,samples=400]{sgn(x)*abs(x+8)**(1/3.0)} \tkzFct[domain=-8:4,line width=0.5mm,samples=400]{abs(x+8)**(1/3.0)}

ToyBoy
  • 117