Now, let's start looking at the code's implementation details.
I believe that beautiful code is short code, and I find that lengthy, complicated code is generally quite ugly. The SGBSV routine is a prime example of the beauty of short code. It begins with a quick verification of the consistency of the input arguments, then continues with two calls that logically follow the mathematical algorithm.
From the first glance, it is obvious what this code is doing: it begins by performing LU factorization with the SGBTRF routine, then solves the system with the SGBTRS routine. This code is very easy to read. There's no need to pore over hundreds of lines of code to understand what the code does. The main task is split into two subtasks, and the subtasks are pushed into a subsystem.
Note that the subsystem adheres to the same design assumptions regarding memory usage as the main system. This is a very important and beautiful aspect of the design.
The routines from the subsystem are reused in different "driver" routines (the SGBSV routine is called a driver routine). This creates a hierarchical system that encourages code reuse. This is beautiful, too. Code reuse significantly reduces the effort required for code development, testing, and maintenance. In fact, it is one of the best ways to increase developers' productivity and reduce their stress. The problem is that reuse is typically difficult. Very often, code is so complicated and difficult to ...