What does 合痕类的个数 (hé hén lèi de gè shù) mean in this mathematics article? From the mathematics article 拉丁阵的枚举和计数(Ⅱ):情形n=4,k〈=4, we have the following first paragraph:



I'm confused about what 合痕类的个数 (hé hén lèi de gè shù) means here (it's used twice).  Google Translate says it means "the number of traces", but I don't feel this is accurate.

Question: What does 合痕类的个数 (hé hén lèi de gè shù) mean in this mathematics article?

My transcription: 


  文献[1]中引人了(n,k)-拉丁阵概念，并对n=2，3的情形给出了(n,k)-拉丁阵和它们的合痕类的个数。本文继续讨论n=4的情形，给出了(4,k,1)-拉丁阵，(4,2),(4,3)-和(4,4)-拉丁阵及它们的合痕类的个数。


My translation:


  In document [1] is the fascinating引人 (short for 引人入胜 (?)) concept概念 of the (n,k)-Latin matrix, and the case情形 of n=2,3, gives (n,k)-Latin matrices and their [合痕类的个数 (?)].  In this paper, we continue继续 the discussion讨论 to the case情形 of n=4, give (4,k,1)-Latin matrices, (4,2), (4,3), and (4,4)-Latin matrices and their [合痕类的个数 (?)].


If it helps, here's an example of what one looks like:
I am absolutely not a mathematician, but here is my stab:

isotropic: "having the same properties in all directions,"

In your case, a regular matrix, your example showing the vertical and horizontal elements to be the same.

合痕：isotropy
合痕类：isotropic
合痕类的个数： isotropic elements / individual elements
矩阵: matrix

本文继续讨论n=4的情形，
This document goes on to discuss n=4 matrices
给出了(4,k,1)-拉丁阵，(4,2),(4,3)-和
showing (4,k,1) - Latin matrices, (4,2), (4,3)- and
(4,4)-拉丁阵及它们的合痕类的个数。
4 by 4 Latin matrices and their isotropic elements