Bounds and Constraints can restrict the parameter values to a specific range, and avoid the parameters wandering into wrong parameter regions. For example, in the exponential growth model:
A value of the parameter t close to zero may cause instabilities. A constraint such as t ≥ 0.1 may prevent the problem.
Parameter Bounds include lower (LB) and upper bounds (UB), both of which can be set directly in the Bounds tab of the NLFit dialog:
Constraints enable you to set linear constraints for the parameters. You can set these constraints in the Constraints box in the Code tab of the NLFit dialog: