RE: Problem with lag variables

Dear UrbanSim Users,

We have fixed the problem with the lag variables. To get this fix,
download and install a Nightly release with a date on or after Sept 1,
2006 from the Download link on
http://www.urbansim.org/opus/opus_manual/docs/.

The Sept 1 version also includes a fix to the unrolling of gridcells
from development_event_history. More details are in our release notes:
http://www.urbansim.org/opus/opus_manual/docs/release_notes.html.

Best regards,

David

________________________________

From: David Socha
Sent: Friday, August 25, 2006 6:13 PM
To: users_at_urbansim.org
Subject: Problem with lag variables

Dear UrbanSim Users,
         
We have discovered that there is a bug in the Opus support for lag
variables. We plan to fix this soon, but wanted you all to know about
it.
         
The details of the problem are as follows. If a lag variable has
dependencies on computed attributes (those attributes whose values are
computed by Opus Variables) the values returned by the lag variables
will always be for the current year, instead of the lagged year. For
example, if we want to compute urbansim.gridcell.population_lag1 for
2001, which depends on persons attribute of HouseholdSet, it *should*
use the HouseholdSet data of year 2000. Unfortunately, it uses the
HouseholdSet data of year 2001. If the dependencies are on primary
attributes (those attributes of an entity that are not created by a
variable), the lag variable will work fine. This bug has been in the
code all along.
         
Best regards,
         
David Socha
Center for Urban Simulation and Policy Analysis
University of Washington
www.urbansim.org
206 616-4495
Received on Fri Sep 01 2006 - 07:51:02 PDT