Ex84-3D-pgfplots.tex

\begin{tikzpicture}[scale=0.32]
  \begin{axis}[
    3d box,
    width=15cm,
    view={25}{25},
    enlargelimits=false,
    grid=major,
    domain=-6:6,
    y domain=-6:6,
    samples=21,
    xlabel=$x_1$,
    ylabel=$x_2$,
    zlabel={$f$}
    ]

    \addplot3 [y domain = -6:6, surf, opacity=0.5, faceted color = yellow] {(x-1)^2+y-2};

    \addplot3 [y domain = -6:6, contour gnuplot = {levels={-0.25},number=14, labels={false}, draw color = black}, samples = 50]
    {(x-1)^2+y-2};

    % \addplot3 [y domain = -5:5, contour gnuplot = {number=14, draw color = black}, samples = 50]
    % {(x-1)^2+y-2};

    % \addplot3[surf, opacity = 0.5, samples =2] {1};

    \addplot3 [contour gnuplot = {levels={1,-0.25,-2.5}, number=14, labels={false}, draw
      color=black}, samples=50, z filter/.code={\def\pgfmathresult{60}}] {(x-1)^2+y-2};

    \addplot3+ [samples=20, no markers, color = red] (x,1+x,60);

    \addplot3+ [samples=20, no markers, color=red] (x,2-x,60);


  \end{axis}
\end{tikzpicture}