Saturday, October 27, 2007

Occam's Razor

William of Ockham (c. 1285–1349) a 14th-century English Franciscan friar is credited with the principle that states that one should not make more assumptions than the minimum needed. This is more commonly known as Occam’s Razor or the principle of parsimony which originates from the Latin phase “lex parsimoniae” or “entia non sunt multiplicanda praeter necessitatem” which translates to “entities should not be multiplied beyond necessity.” This is a principle perhaps better known as KISS or "keep it simple, stupid."

Some examples of this principle in engineering:

As the part count increases for a design, the reliability generally decreases. For example, a bracket that uses bolts to attach it to another structure will have lower reliability if 4 smaller bolts are used rather than 2 larger bolts if each bolt has the same safety factor and hence the same probability of failure.

A design load with a 20% uncertainty used in a sophisicated computer simulation with high precision results will have no better certainty than 20%. Select the simulation method based on the level of certainty of the model parameter certainties.

Sensors have failure modes. Will a sensor used to monitor a design function improve the overall reliability when considering the sensing reliabilities?

Regression models should always be checked against first principles and limiting conditions. If they fail this review then the model and/or data is likely wrong. The simpliest regression model should always be used and in many cases will be linear.

Test data should always be used in the context of the test and measurement methods. It is very difficult to simulate the real world useage in the laboratory.

A simple test is better than no test as long as the context of the test and quality of the data are understood.

The first calculation ever made for any concept and idea should be by pencil on a single sheet of paper. Anything more is a waste of time. If the concept doesn't pass the first principle test it doesn't have a chance of passing a sophisicated computer simulation.