I would like to know if it is possible to add a linear constraint of the type:

Yfit[x=23] - Yfit[x=12] < mydata_b[x=23]- mydata_b[x=12]

where the EXTREME peak width between two definite points is constraint to the difference at the same x values of the fitted data.

If it is possible could you please tell me how i can do it!

When enabled, the General Linear Constraints field in the nonlinear curve fitter must include at least one parameter reference. Unfortunately, since the constraint you would like to impose does not specifically contain a parameter, it will not work.

Your best bet would be to constrain the parameter called w. For instance, according to your example, w should be constrained to 11 (the difference between 23 and 12). This type of constraint could easily be accomplished by using the Lower and Upper Bounds features instead of the General Linear Constraints text box.

Sincerely,
Ryan Toomey