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Allow using tanh-sinh quadrature for table building

Xiaoyu Wei requested to merge tanh-sinh into master

This PR adds two options special_radial_brick_quadrature and nradial_brick_quad_points to the Droste class of table builders that enable using tanh-sinh quadrature in the radial direction.

Example usage:

from sumpy.kernel import LaplaceKernel
import numpy as np
import pyopencl as cl

import volumential.nearfield_potential_table as nft

knl = LaplaceKernel(2)
ctx = cl._csc()
queue = cl.CommandQueue(ctx)
q_order = 5

table = nft.NearFieldInteractionTable(q_order, sumpy_kernel=knl)
table.build_table_via_droste_bricks(
    n_brick_quad_points=200, alpha=0., use_symmetry=True,
    nlevels=1, queue=queue, adaptive_quadrature=True,
    special_radial_brick_quadrature=True, nradial_brick_quad_points=200)

One direct improvement using tanh-sinh quadrature is to be able to attain high accuracy for non-1/r type (e.g. logarithmic) kernels. In the case of 2D Laplacian kernel, it roughly improves the accuracy from 7 decimal places to 14.

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