Module 14
Sensitivity and design-space exploration
Which inputs the answer actually depends on — and why a wide plausible range beats a large exponent.
What this module covers
- Distinguish an uncertain input from a design variable
- Compute an elasticity and check it against the exponent in the algebra
- Rank variables by swing rather than by elasticity, and say why
- Bracket an answer with corner combinations, and say when that is invalid
- Recognise a non-monotonic response and what it costs you
- Justify a plausible range rather than assuming a percentage
Lessons
Elasticity, swing, and the ranking that surprises people the first time they compute it.
Start lesson →Three runs that bound an answer, the assumption they rest on, and what happens when it fails.
Start lesson →
Module checkpoint
Check what you have taken in
3 questions
Question 1
Which input should a sensitivity study direct the most effort at narrowing?
Question 2
A beam's deflection goes as 1/d³ where d is the depth. The depth could be 400, 457 or 533 mm. Taking 457 as the base, by what factor does the deflection change if the 400 mm section is used instead? Give the factor to two decimal places.
Question 3
An output has an elasticity of −0.5 with respect to mass. Mass could be 20 % higher than assumed. By what percentage does the output change? Give the magnitude of the change.