FLremdoublevertex

by Tim C. Lueth, SG-Lib Toolbox: SolidGeometry 5.6 - Auxiliary function
Introduced first in SolidGeometry 4.2, Creation date: 2018-08-14, Last change: 2025-09-14

returns the indices of a FL that a double entry vertex index

Description

If in a Facet list there exist a degenerated traingle such as [1 1 2] or [1 2 1]
this facet is found by this function.
fi=FL(:,1)==FL(:,2) | FL(:,1)==FL(:,3) | FL(:,2)==FL(:,3);

Example Illustration

Syntax

fi=FLremdoublevertex(FL)

Input Parameter

FL: Facet list

Output Parameter

fi: removal facet index

Examples


FLremdoublevertex([1 2 3;3 2 1;2 1 2; 4 2 4])

Copyright 2018-2025 Tim C. Lueth. All rights reserved. The code is the property of Tim C. Lueth and may not be redistributed or modified without explicit written permission. This software may be used free of charge for academic research and teaching purposes only. Commercial use, redistribution, modification, or reverse engineering is strictly prohibited. Access to source code is restricted and granted only under specific agreements. For licensing inquiries or commercial use, please contact: Tim C. Lueth

Algorithm (Workflow)

This function, FLremdoublevertex, is designed to identify degenerate triangles within a facet list (FL). A degenerate triangle is one where two or more vertices are the same, such as [1 1 2] or [1 2 1].

Input Parameters

FL: A matrix representing a list of facets. Each row corresponds to a triangle, with three columns representing the indices of the vertices that form the triangle.

Output Results

fi: A logical array indicating which rows (facets) in the input matrix are degenerate. A value of true means the corresponding facet is degenerate.

Algorithm Explanation

The function works by evaluating each row of the input matrix FL to check for degenerate triangles. It does this by comparing the vertex indices within each row:

FL(:,1)==FL(:,2): Checks if the first and second vertices are the same.
FL(:,1)==FL(:,3): Checks if the first and third vertices are the same.
FL(:,2)==FL(:,3): Checks if the second and third vertices are the same.

The logical OR operator (|) is used to combine these conditions, resulting in a logical array fi where each element is true if any of the conditions are met for the corresponding row, indicating a degenerate triangle.

Example

Consider the following example:

FLremdoublevertex([1 2 3; 3 2 1; 2 1 2; 4 2 4])

In this example, the function will return a logical array indicating which rows contain degenerate triangles. The third row [2 1 2] and the fourth row [4 2 4] are degenerate, so the output will be:

[false; false; true; true]

Algorithm explaination created using ChatGPT on 2025-08-18 22:41. (Please note: No guarantee for the correctness of this explanation)

Last html export of this page out of FM database by TL: 2025-09-21