software bugs

Some disasters attributable to bad numerical computing
"Program testing can be used to show the presence of bugs, but never to show their absence!" Edsger Dijkstra

and

- If debugging is the process of removing software bugs, then programming must be the process of putting them in.
Edsger Dijkstra

Some disasters attributable to bad numerical computing

Have you been paying attention in your numerical analysis or scientific computation courses? If not, it could be a costly mistake. Here are some real life examples of what can happen when numerical algorithms are not correctly applied.
The Patriot Missile failure, in Dharan, Saudi Arabia, on February 25, 1991 which resulted in 28 deaths, is ultimately attributable to poor handling of rounding errors.
The explosion of the Ariane 5 rocket just after lift-off on its maiden voyage off French Guiana, on June 4, 1996, was ultimately the consequence of a simple overflow.
The sinking of the Sleipner A offshore platform in Gandsfjorden near Stavanger, Norway, on August 23, 1991, resulted in a loss of nearly one billion dollars. It was found to be the result of inaccurate finite element analysis.
Last modified August 26, 1998 by Douglas N. Arnold, arnold@ima.umn.edu

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In 1969 in Rome, Dijkstra spoke to Joel Aron (not Eyles), "head of IBM's Federal Systems Division which had been responsible for the software of the moonshot". It wasn't specifically in the lunar module, but somewhere in the 40,000 LoC. However, the bug was that the moon was repelling; and it was found by accident, 5 days before launch. Dijkstra said to Joel Aron "How do you that? Do what? - Joel asked. Getting that software right! - Dijkstra answered "
Right?! - he said that in one of the calculations of the orbit of lunar module the Moon have been defined repelling instead of attracting.
They have bee discovered this error by accident!
Imagine by accident.. by ACCIDENT, five days before the shot!
Dijkstra went white and said: "Those guys have been lucky!"
Yes - Joel Aron agreed.
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Joel D. Aron
Federal Systems Division, Federal Systems Center, Gaithersburg, Maryland.
Military engineering (U. S. Military Academy, B.S., 1948). Joined IBM in 1954. Bas had a variety of technical, managerial, and consulting assignments in applied science and development, with emphasis on defense and scientific systems.
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