It is all part of linear algebra.
represents eight simultaneous equations: four terms in the first, third, fourth, and sixth equations, two terms in the second, fifth, seventh and eighth equations.
What is passed to the subroutine is the address of the structure of the leftmost term in the equation. All equations are arranged in a flat file.
The subroutine subtracts each term in the first line from the (expanded) four terms in each of the following three lines.
The result of that operation is

This is the actual output of the program.

If linear algebra is foreign to you, then you will have trouble understanding the program.

QUOTE=ntubski;6484948]I don't understand what format you are using here, or how this relates to the actual output of the program.[/QUOTE]

I guess that is in some abstract sense the output of the program. But how does it relate to what the program prints to stdout? (E.g., what NevemTeve posted?)

I learned about it once, but it's been a while.