3

I have written the following code.

MWE

\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{tikz}
\usepackage{pgfplots}\pgfplotsset{compat=1.18}

\author{Some dude's name}
\begin{document}
\begin{tikzpicture}
\begin{axis}
[
    xlabel={x}, 
    ylabel={y}, 
    grid, 
    ticks=30
]
\draw [thick, blue] (rel axis cs:0.5,0,0) -- (rel axis cs:0.5,1,0);
\addplot3[blue, no marks, surf, domain=0:1, samples=50] {25-5*x*x -y*y};
\draw [thick, red] (rel axis cs:0.5,0,0) -- (rel axis cs:1,0.5,0);
\end{axis}
\end{tikzpicture}
\end{document}

Current outout + my texmaker window

scrnsht

what I need(edited with MS paint, Purple colour = a line, a curved line and a arc)

enter image description here

One can notice the Red and the blue \draw near addplot 3.

I want to erase it(delete that lines) and draw a line, a curved line and a arc like above

2
  • Well, to erase those, just remove the lines I suggested in tex.stackexchange.com/a/606645/38080. Then find the coordinate you want (in the graph x,y,z coordinate system) and just draw them using TikZ command. If the curved line is just a line in the surface, you can use a 3d line graph (another addplot with a null y-domain).
    – Rmano
    Jul 27 at 14:01
  • @Rmano can you give me relevant page numbers for to do above things?
    – Gomesz785
    Jul 27 at 16:01
3

This is what I would do --- then you can add things and change the coordinates (you will need to calculate where do you want your lines to go, exactly). I heavily commented the code to give you a lot of "fish lines" to catch your own fish.

\documentclass[12pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{pgfplots}\pgfplotsset{compat=1.18}

\begin{document}
\begin{tikzpicture}
\begin{axis}
[
    % explicitly specify axis limits
    xmin=0,xmax=1,ymin=0,ymax=1,zmin=18,zmax=26,
    xlabel={x},
    ylabel={y},
    grid,
    % do not clip the \draw commands and clip each
    % addplot to its domain
    clip mode=individual,
]
% line on the xy plane (that way goes behind the surface)
% we mark a point at 30% of the line
\draw[thick]  (0.4,0,18) -- (0.4,1,18) coordinate[pos=0.3](a);
% main surface
\addplot3[blue, no marks, surf, domain=0:1, samples=10] {25-5*x*x -y*y};
% graph restricted at at y=0.3 (parametric curve format)
\addplot3[ultra thick, no marks, domain=0:1, samples=10, samples y=1] (x, 0.3, 25-5*x*x -0.3*0.3);
% line  touching the parabola
\draw[thick]  (0.4,0,18) -- (0.4,0.3,25-5*0.4*0.4-0.3*0.3) coordinate[pos=0.3](b);% coordinate on the black parabola
% draw spline and angle label
% in and out are the angle at which the curve leaves the final and initial point
\draw[thick,->] (a) to[out=100, in=-10]  node[midway, above right]{$\alpha$} (b);

\end{axis}
\end{tikzpicture}
\end{document}

enter image description here

You maybe prefer to have the surface semi-transparent, to better convey the meaning of the arc:

\documentclass[12pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{pgfplots}\pgfplotsset{compat=1.18}

\begin{document}
\begin{tikzpicture}
\begin{axis}
[
    % explicitly specify axis limits
    xmin=0,xmax=1,ymin=0,ymax=1,zmin=18,zmax=26,
    xlabel={x},
    ylabel={y},
    grid,
    % do not clip the \draw commands and clip each
    % addplot to its domain
    clip mode=individual,
]
% line on the xy plane (that way goes behind the surface)
% we mark a point at 30% of the line
\draw[thick]  (0.4,0,18) -- (0.4,1,18) coordinate[pos=0.3](a);
% line  touching the parabola
\draw[thick]  (0.4,0,18) -- (0.4,0.3,25-5*0.4*0.4-0.3*0.3) coordinate[pos=0.3](b);% coordinate on the black parabola
% main surface, semi-transparent
\addplot3[blue, no marks, surf, domain=0:1, samples=10, opacity=0.7] {25-5*x*x -y*y};
% graph restricted at at y=0.3 (parametric curve format)
\addplot3[ultra thick, no marks, domain=0:1, samples=10, samples y=1] (x, 0.3, 25-5*x*x -0.3*0.3);
% draw spline and angle label
% in and out are the angle at which the curve leaves the final and initial point
\draw[thick,->] (a) to[out=100, in=-10]  node[midway, above right]{$\alpha$} (b);

\end{axis}
\end{tikzpicture}
\end{document}

enter image description here

9
  • Best. I feel like we are communicting brain-to-brain.
    – Gomesz785
    Jul 27 at 15:59
  • 1
    ;-) if you did post this question straight on it would have been much faster... I think this is a clear example of meta.stackexchange.com/questions/66377/what-is-the-xy-problem
    – Rmano
    Jul 27 at 16:13
  • did you mean to ask the series of problems I asked today as a one? or improve the structure of the this question?
    – Gomesz785
    Jul 27 at 16:15
  • 1
    I thought that the series of problem where just an attempt to obtain this graph. If you just posted the original graph with the added lines with MSPaint, I could have posted this answer directly ;-). No harm done, really.
    – Rmano
    Jul 27 at 16:20
  • 1
    No harm for neither! ;-)
    – Rmano
    Jul 27 at 16:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.