I am using NIntegrate to integrate a 3-dimensional region. When I don't set any integration options, I get a warning
The global error of the strategy GlobalAdaptive has increased more than 2000 times ... Increasing the value of the GlobalAdaptive option MaxErrorIncreases might lead to a convergent numerical integration
In a similar question, Can you use "MaxErrorIncreases" when numerically integrating over a region? Michael E2 suggests using the "FiniteElement" method. This integrates nicely, or at least there are no warnings or errors.
The Finite Element User Guide is very detailed but it seems to say nothing about using finite elements with NIntegrate. Neither the NIntegrate help page or the Advanced Numerical Integration guide seem to mention the method FiniteElement. Maybe it's there but I didn't find it. I would like to explore refining the mesh to check convergence but I can't find any information about how to give NIntegrate options for the FiniteElement method.
Can anyone provide or point me to some guidance on using a finite element mesh with NIntegrate?
Edit:Looking some more at the Finite Element User Guide, I see that there is a section on how to pass options for ElementMesh creation to NDSolve. I tried the same syntax for NIntegrate, setting MaxCellMeasure, and Mathematica doesn't complain, and the answer changes a bit and then converges, so maybe that works. Any confirmation would be appreciated.
Edit2: Thanks for your comments. The function I want to integrate is
f[x_, y_, z_] = (x^4 y - 2 x^3 x2 y + y^5 - 2 y^4 y2 + y^3 y2^2 +
11 y^3 z^2 - 14 y^2 y2 z^2 + y y2^2 z^2 + 10 y z^4 - 3 y2 z^4 +
x2^2 (y^3 - 8 y z^2) - 8 y^3 z z2 + 12 y^2 y2 z z2 -
17 y z^3 z2 + 3 y2 z^3 z2 - 2 y^3 z2^2 + 7 y z^2 z2^2 +
x x2 (-2 y^3 + 9 y2 z^2 + y z (-11 z + 18 z2)) +
x^2 (x2^2 y + 2 y^3 - 2 y^2 y2 - 3 y2 z (z + 2 z2) +
y (y2^2 + 11 z^2 - 8 z z2 - 2 z2^2))) /(32 \[Pi]^3 (x^2 + y^2 +
z^2)^4 ((x - x2)^2 + (y - y2)^2 + (z - z2)^2)^(5/2))
where x2, y2, z2 are O(1) parameters and I want to integrate over many values of the parameters. The region is
region = RegionDifference[RegionDifference[FullRegion[3], Ball[{0, 0, 0},ε]],
Ball[{x2, y2, z2}, ε]]
I am interested in the limit ε << Norm[x2vector], where x2vector = {x2, y2, z2}. The integration command, without any options is
NIntegrate[f[x, y, z], {x, y, z} ∊ region]
with x2, y2, z2, and ε replaced with numbers.