faq 152764417

Mode/alternative specific constants

by Ecaterina McCormick on 2018-01-15 15:58:32

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I am unclear where the alternative-specific constants are being set.  Each mode includes the following lines:

<!-- [utils] alternative-specific constant.  no guarantee that this is used anywhere. default=0 to be backwards compatible for the time being -->

<param name="constant" value="0.0" />

Why does the code preceding the setting of the alternative specific constant say “no guarantee that this is used anywhere”?

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Comments: 1

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Re: Mode/alternative specific constants

by Kai Nagel on 2018-01-15 21:39:32

At some point, we revised the config parameters, and at that point we put in the alternative-specific constant since we knew that at some point we would need it, but it was indeed not used anywhere.

Now it is used, as you can verify from CharyparNagelLegScoring .

A remaining problem is that this constant is used per leg. So if, say, you walk to train, take train, walk to bus, take bus, walk to work, the alt-spec constant of walk is added three times.

In contrast, there is some correction for the alternative-specific constant of pt, so that is in fact only added once even in a trip that has multiple pt legs.

(Again check in CharyparNagelLegScoring .)

If you want to control these things in detail, best write your own scoring function.