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The command is

Volume[Region[ImplicitRegion[{Sqrt[x^2+y^2]<=Abs[Sin[z]],0<=z<=2Pi},{x,y,z}]]]

The computation time is exceeding my expectation. The Integral is solvable by hand (I don't want to say I'm better than the kernel $\tiny \text{lol}$, just that it's solvable).

E.g. the command

Volume[Region[ImplicitRegion[{Sqrt[x^2+y^2]<=Abs[z],0<=z<=2Pi},{x,y,z}]]]

results in $\tfrac{8\pi^4}{3}$.

Question: Is it normal that the kernel is taking so long to compute? If not, why is it stuck?

Attempt: My guess is that sin is somehow causing the problem, but I don't know why it would.

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  • 1
    $\begingroup$ Just for info. reg = ImplicitRegion[{Sqrt[x^2 + y^2] <= Sin[z], 0 <= z <= Pi}, {x, y, z}];Volume[reg] // Timing results in {915.422, 4.92673} (13,3,1 on Windows 10). $\endgroup$
    – user64494
    Commented Sep 22, 2023 at 20:27

3 Answers 3

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If I replace 0 by 0. in your inequality for z, it completes fairly quickly.

In[6]:= Volume[
 Region[ImplicitRegion[{Sqrt[x^2 + y^2] <= Abs[Sin[z]], 
    0. <= z <= 2 Pi}, {x, y, z}]]]


(* Out[6]= 9.8696 *)

Using 0. instead of 0 converts this to a numerical problem, instead of asking for a symbolic solution, which may take a very long time to compute.

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For revolution 3D, it is recommend to help Mathematica to calculate its volume by the formula, that is, for every 2D region reg, we rotate it around the InfiniteLine[{{0, 0}, {0, 1}}] to get 3D revolution,to calculate the volume,we accumulate the 2D ring for all point {x,y} in the 2D region.

revolutionVolume[reg_] := 
 Integrate[
  2 π*RegionDistance[InfiniteLine[{{0, 0}, {0, 1}}]]@{x, y}, {x, 
    y} ∈ reg]
  • 2D regions.
reg1 = ImplicitRegion[{0 <= x <= y, 0 <= y <= 2 π}, {x, y}];
reg2 = ImplicitRegion[{0 <= x <= Abs[Sin[y]], 0 <= y <= 2 π}, {x, 
    y}];
reg3 = Disk[{0, 0}, 1, {-π/2, π/2}];
RegionPlot[#, AspectRatio -> Automatic] & /@ {reg1, reg2, reg3}

revolutionVolume /@ {reg1, reg2, reg3}

enter image description here

{(8 π^4)/3, π^2, (4 π)/3}

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$Version

(* "13.3.1 for Mac OS X ARM (64-bit) (July 24, 2023)" *)

Clear["Global`*"]

RegionPlot3D[Sqrt[x^2 + y^2] <= Abs[Sin[z]],
 {x, -1, 1}, {y, -1, 1}, {z, 0, 2 Pi},
 BoxRatios -> {1, 1, Pi}]

enter image description here

rgn = ImplicitRegion[{Sqrt[x^2 + y^2] <= Abs[Sin[z]], 0 <= z <= 2 Pi}, 
   {x, y, z}];

Calculate the volume using less than infinite precision

(vol = Volume[rgn, WorkingPrecision -> 17] // N) // AbsoluteTiming

(* {9.39592, 9.8696} *)

vol = RootApproximant[vol/Pi^2]*Pi^2

(* π^2 *)
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