Sort out usage of "specifications" versus "requirements" (and index specifications)

[Richard Murray]

On 16 Mar 2018, Karl said:

• I suddenly got uncertain about the words requirements and specifications, looking at the dictionary I am still confused. The reason is that I think it would be useful to include Fig 15.2 and the associated text in Chapter 12, it adds about a page but I think it would be a nice addition to Section12.3. In Ch 12 we talk a lot about requirements. What do you think?

RMM response:

• For requirements vs specifications, I’m not sure that I have a good rule for when to use what. I think that specifications are a bit “softer” than “requirements”, though in many cases they can be used interchangeably. Let me look through the book and see if there is any consistency of the way we currently use these terms and whether we can come up with some consistent pattern to use.

[Richard Murray]

Also need to make sure that specifications and requirements both appear in the index properly.

[Richard Murray]

Definitions:

• Requirements: thing that is needed, must be satisfied
• Specification: an act of describing or identifying something precisely or of stating a precise requirement

Not clear how to distinguish (nor how to index).

[Richard Murray]

Went through and checked all uses of specifications and requirements. I tried to use the rubric that a requirement is something absolute and perhaps higher level (eg, stability), while a specification is a more detailed description of a properties (eg, performance specifications given through bounds on the sensitivity function).

Updates in commit f546237.