Question

Does not display NominalCoefficient when AIMMS Linear Presolve is off?

  • 6 January 2021
  • 4 replies
  • 47 views

I’m trying to see the nominal coefficients property for a variable. I have CoefficientRange property selected and my  Calculate Sensitivity Ranges is ON. However, it doesn’t show the property when the problem is solved with AIMMS Linear Presolve being OFF? Please advise.

 

Here’s the documentation I found:

.NominalCoefficient Definition: When the property CoefficientRange of a variable is set and the option Calculate Sensitivity Ranges is not set to off a coefficient range sensitivity analysis is conducted such that the optimal basis remains constant. As a result of this analysis the variable suffix .NominalCoefficient contains the nominal objective coefficient value.


4 replies

Userlevel 3

Please note that the coefficient range sensitivity analysis is only available for LP models (and not for MIP nor nonlinear models).

If the coefficient range sensitivity analysis could be conducted then the .NominalCoefficient suffix (normally) contains the coefficient of the variable in the objective. If variable X has no coefficient in the objective then X.NominalCoefficient will be 0.

Your post seems to suggest that you get non-zero values for .NominalCoefficient if the option Linear Presolve is switched on; is that the case?

 

Userlevel 6

Also, where are you trying to find the results. E.g. the data page can show them by selecting the right suffix. See below in a simple example where Transport is a variable in my model:

 

 

“Your post seems to suggest that you get non-zero values for .NominalCoefficient if the option Linear Presolve is switched on; is that the case?”

Yes, this is the case. What’s interesting is that if I use a more updated version of AIMMS, 4.69 compared to 4.37. I see that 4.69 populates the NominalCoefficient values as expected when Presolve is OFF. Did something change between versions? Is it actually doing presolve with 4.69 even though it’s OFF? 

I expect NominalCoefficient to be there since the it’s in the objective. I’m trying to see it in the math inspector but normally it’d be in the data page, either or. 

 

 

Userlevel 3

Several changes have been made between versions 4.37 and 4.69 but we did not change anything in particular for .NominalCoefficient. I do not know which change would explain the changed behavior but the good news is that in the later version it seems to work as expected.

If your model is linear and the option Linear Presolve is switched off then AIMMS will not use the presolver.

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