Pgfplots: embedding a line in a surface
Pgfplots: embedding a line in a surface
I want to draw an identity across a surface plot. This identity should start at the bottom left, and end at the top right (from tip to tip). With the axis I've given (see below), the v_1=2(v_2-20). This becomes y=2(x-20) given the way the axes are defined. I've tried plotting this in various ways, but it does not seem to work on top of the 3d surface.
beginfigure[h]
begintikzpicture[scale=2]
beginaxis[
title=secret research,
xlabel=$v_2$, ylabel=$v_1$,
small,
x dir=reverse
]
addplot3[
surf,
domain=0:20,
domain y=0:10,
]
((y^2/(0.5*(x+y))/20);
endaxis
endtikzpicture
(x,2*(x-20))
@marmot Sorry for it being unclear. I would like to plot the identity that maps across the surface diagonally from v_2=20 to v_1=10. This would be a single function, not a surface, as it is defined at one particular intersection of the v_2 and v_1 axes.
– pafnuti
Sep 15 '18 at 14:41
You want a one-dimensional plot, i.e a line, then? At which z-value should this line be? Should it really be
v_1=2(v_2-20), i.e. at v_1=0 v_2 will be -40, ie. far off from the surface?– marmot
Sep 15 '18 at 14:51
v_1=2(v_2-20)
v_1=0
v_2
@marmot Yes one-dimensional, at the z-value of the surface.
– pafnuti
Sep 15 '18 at 14:56
1 Answer
1
I hope I guess correctly.
documentclass[tikz,border=3.14mm]standalone
usepackagepgfplots
pgfplotssetcompat=1.16
begindocument
begintikzpicture[scale=2,declare function=f(x,y)=((y*y/(0.5*(x+y))/20);]
beginaxis[
title=secret research,
xlabel=$v_2$, ylabel=$v_1$,
small,
x dir=reverse
]
addplot3[
surf,
domain=0:20,
domain y=0:10,
]
(f(x,y);
addplot3[mesh,domain=0:10,point meta=0] (2*x,x, (f(2*x,x));
addplot3[mesh,domain=0:10,point meta=0.5] (2*(10-x),x, (f(2*(10-x),x));
endaxis
endtikzpicture
enddocument
Of course, you can choose whatever color you like for those lines.
documentclass[tikz,border=3.14mm]standalone
usepackagepgfplots
pgfplotssetcompat=1.16
begindocument
begintikzpicture[scale=2,declare function=f(x,y)=((y*y/(0.5*(x+y))/20);]
beginaxis[
title=secret research,
xlabel=$v_2$, ylabel=$v_1$,
small,
x dir=reverse
]
addplot3[
surf,
domain=0:20,
domain y=0:10,
]
(f(x,y);
addplot3[mesh,domain=0:10,color=red] (2*x,x, (f(2*x,x));
addplot3[mesh,domain=0:10,color=black] (2*(10-x),x, (f(2*(10-x),x));
endaxis
endtikzpicture
enddocument
That's exactly what I want, but from the left-most point at (v_1=0,v_2=20,z=0) to the rightmost (v_1=10,v_2=0, z approx 1). Will change it myself :)
– pafnuti
Sep 15 '18 at 15:01
@pafnuti I add that one. There is one potential piftfall: you need to use mesh since otherwise there will be a closed cycle.
– marmot
Sep 15 '18 at 15:04
Does this mean I can't choose an arbitrary colour for the line? Because of the point meta colour map?
– pafnuti
Sep 15 '18 at 15:52
@pafnuti You can choose whatever color you like, I added an update.
– marmot
Sep 15 '18 at 15:57
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I am sorry, I do not understand the question. Could you please make more explicit what you mean? What does "This becomes y=2(x-20) given the way the axes are defined. " mean? Do you just want to plot
(x,2*(x-20))? But this is a 3d plot.– marmot
Sep 15 '18 at 14:31