Intersection near a branch cut causes problems

[chan-y-park]

When two S-walls intersect near a branch cut, the joint-finding algorithm look for the index of the z-coordinate nearest to the intersection point for each S-wall, not inserting the intersection point into the S-walls. This z-coordinate is then used to read out the local root of the S-wall.

Then, sometimes the z-coordinate found by the algorithm is the z-coordinate of the intersection of the S-wall and a branch cut, which is inserted before looking for a joint. The root classification on the branch cut is intrinsically ambiguous, so this results in an incorrect spawning of a descendant S-wall.

One way to prevent this is first insert an intersection point to the two parents wall, compare its location with that of the branch cut to figure out the correct local root, then use the joint-finding algorithm.

Or we can increase the numerical accuracy when such a problem happens, but this is costly.

This is not a fundamental problem but a numerical one, so it appears sporadically, which can be safely ignored when studying the data, but it would be better to fix this problem so that it won't mask other issues that may look similar but have fundamental importance.

[chan-y-park]

fixed in 6aa4d6d