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I wanted to draw a "cap"-like paraboloid structure.

like this one ...

enter image description here

.

But, the function $$f(x, y) = -x^2-y^2+4$$
is giving me a "tent"-like structure.

enter image description here

See the link.

How should I modify my equation/function to achieve this?

user366312
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  • Unless there is a particular constraint, I see no reason you couldn't just turn each $z$ into $-z$ - which would be achieved by multiplying through the equation $f$ by $-1$. – PrincessEev Dec 28 '18 at 11:22
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    You can make it “steeper” by either including a constant in front of $x^2$ and $y^2$ or use fourth/sixth powers instead – b00n heT Dec 28 '18 at 11:22
  • @EeveeTrainer, up-side down part is easy. converting tent to a cap is the hard part. – user366312 Dec 28 '18 at 11:24
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    Why do you think that the picture below does not represent what you want? Is it just the drawing limits of the axes? Also, the meshing is done differently. – Matti P. Dec 28 '18 at 11:24
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    The issue is the domain of the plot, it is plotted over a circle for the "cap", and over a square for the "tent": this fixes it somewhat – Wouter Dec 28 '18 at 11:27

1 Answers1

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generally $z=ax^2+by^2+c$ plots that paraboloid shape.the higher the magnitudes of a and b are the higher stiff the graph gets.change in c changes the vertical distance.if a and b are negative then the graph flips its face like your case.

to get your desired shape,it is just needed to change the sign of your coefficient "a","b".make them positive.you can make them higher in magnitude to get a stiffer graph...or simply you can change the domain(make it larger) of "x" and "y" in your plotting function to have a stiffer look .

Rakibul Islam Prince
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