Sifting algorithm for group generated by a set On page 38 of  "Lecture Notes in Computer Science" by Christoph M. Hoffmann, there is an algorithm (ALGORITHM 2).

I have some confusions.



Why it is written that an entry $M_{i,j}, j &lt; i$, cannot be referenced? what is the meaning  of "reference" here?

Thanks.
One possible explanation is that it is indicating that you should never try to read or use any matrix element $M_{i,j}$ where $i&lt;j$.  "Referenced" might be talking about "de-referencing" a pointer, i.e., reading a memory cell, i.e., reading an entry of the matrix.  Perhaps the text is indicating that the matrix entries $M_{i,j}$ are only defined for $i \ge j$.

I suggest you read the text with this possible perspective in mind and see if it seems consistent with the surrounding context.