Agfdhyk

I am basically trying to make this figure in Tikz only better, but I can't figure out how to make the vertical lines from the x-axis to the graphs M(x). The function is M(x)=−1/2·q·x^2+1/2·q·L·x, where the values of q and L doesn't matter in the first place.

(The figure is made in Maple 2018. It hints at the mistakes made in the vertical lines.)

This is a very 'hacky' solution, and I'm sure some people will be able to give you a more elegant answer, but this definitely works!

I also like it because it's been a very broadly applicable technique for me (especially using intersections).

MWE:

documentclass{article}

usepackage{amsmath}

usepackage{tikz}

usetikzlibrary{calc,intersections}



begin{document}

    begin{tikzpicture}

    draw[<->] (0,6) node[above]{M}--(0,0)--(9,0)node[right]{L};

    draw[name path = C] (0,0) .. controls (3,6) and (5,6) .. (8,0) node[pos = 0.5, above] {$M_{max} = dfrac{1}{8} cdot q cdot L^2$};



    foreach i in {0,0.5,...,8}{

        draw[draw opacity = 0, name path = L] (i,0)--(i,6);

        draw [name intersections ={of = L and C}] let p1 = (intersection-1) in (x1,y1)--(x1,0);

    }

    end{tikzpicture}

end{document}

Output:

PS: If you need the curve to look differently, just edit the code for draw[name path = C].... For instance, by changing it to:

draw[name path = C] (0,0) .. controls (2,4) and (6,4) .. (8,0) node[pos = 0.5, above] {$M_{max} = dfrac{1}{8} cdot q cdot L^2$};

you get this (which is closer to your original image). I illustrated this just in case you wanted to see a sample of how to draw curves. :)

As I mention in a comment, a ycomb plot can be used for this. Here are two examples, the first a modified version of marmot's code, the second a more verbose (and probably more complicated than it needs to be) version using pgfplots.

documentclass[border=5mm]{standalone}

usepackage{pgfplots}

pgfplotsset{compat=1.3}

begin{document}

begin{tikzpicture}[

  declare function={

    M(x) = 4-(x-4)*(x-4)/4;

  }

]

draw[latex-latex] (0,6) node[left] {$mathbf{M}$} |- (8.5,0) node[below]

{$mathbf{L}$};

  draw[thick] plot[variable=x,domain=0:8,smooth] ({x},{M(x)});

  draw[thick] plot[variable=x,domain=0:8,ycomb] ({x},{M(x)});

end{tikzpicture}



begin{tikzpicture}

begin{axis}[

  declare function={

    t = 2;

    mid = 5;

    d=4.5;

    M(x) = -(x-mid)^2*(t/d^2) + t;

  },

  axis lines=middle,

  xtick=empty, ytick=empty,

  ylabel=$M$, xlabel=$L$,

  enlarge x limits,

  enlarge y limits={value=0.5,upper},

  domain=mid-d:mid+d

]



addplot [thick] {M(x)} node[midway, above] {$M_{max} = frac{1}{8} qL$};

addplot [ycomb, samples=15] {M(x)};

end{axis}

end{tikzpicture}



end{document}

Here is one more possibility: use a pattern. And if you use clip, as suggested by @nidhin, I'd use a grid rather than a foreach loop. In fact, if you use foreach, since the function is known, you do not need clip.

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{patterns}

usepackage{amsmath}

begin{document}

begin{tikzpicture}

draw[latex-latex] (0,6) node[left] {$boldsymbol{M}$} |- (8.5,0) node[below]

{$boldsymbol{L}$};

draw[thick,pattern=vertical lines] plot[variable=x,domain=0:8,smooth] ({x},{4-(x-4)*(x-4)/4});

end{tikzpicture}



begin{tikzpicture}

draw[latex-latex] (0,6) node[left] {$boldsymbol{M}$} |- (8.5,0) node[below]

{$boldsymbol{L}$};

draw[thick] plot[variable=x,domain=0:8,smooth] ({x},{4-(x-4)*(x-4)/4});

clip plot[variable=x,domain=0:8,smooth] ({x},{4-(x-4)*(x-4)/4});

draw (0,0) grid[xstep=1cm,ystep=6cm] (8,5);

end{tikzpicture}

end{document}

Using clip

documentclass{standalone}

usepackage{amsmath}

usepackage{tikz}

begin{document}

    begin{tikzpicture}[>=latex]

    draw(4,5) node {$M_{max} = dfrac18 cdot q cdot L^2$};

    draw[<->] (0,6) node[above]{M}--(0,0)--(9,0)node[right]{L};

    draw[clip] (0,0) .. controls (3,6) and (5,6) .. (8,0) --cycle;

    foreach i in {0,0.5,...,8}

    draw (i,0) -- ++ (0,10);

    end{tikzpicture}

end{document}