Re: [UrbanSim-Users] location choice models: problem with sampling alternatives

Hi Liming,

I made a mistake. I wanted an indicator that would show me vacant
commercial units by gridcell, especially those gridcells that had
negative vacancies. To do this, I modified the function
opus_core.misc::clip_to_zero_if_needed so that it would not clip to
zero.

After computing the indicator, but before running the Eugene model and
our own model, I forgot to revert clip_to_zero to its correct behavior.

Your answer was correct. I was the culprit. Sorry for the confusion.

Now for a legitimate question. In our model, as well as in the Eugene
model, we're seeing what seems to be a high number of unplaced jobs
being placed by the Distribute Unplaced Jobs Model. Put more
concretely, in both models, there are roughly 75,000 total jobs in the
base year, and we're seeing on the order of 3,000 to 4,000 unplaced
jobs at times throughout the simulation.

My question is, is this "normal"? Is there an accepted threshold for
a reasonable number of jobs that cannot be placed by ELCM?

Also, in our model, we're seeing an accumulation of negative job space
vacancy as time progresses. Does the developer model try to develop
more job space, by building non-residential square footage, in areas
that currently have negative job space?

Thanks,

Brian

On May 2, 2008, at 3:23 PM, Liming Wang wrote:

> Brian,
> This means the array used as weight in the weighted sampling contains
> negative (less than 0) values. In most case, the weight array is from
> vacant units attribute, which could contain negative values if more
> households are allocated to gridcells/buildings than their existing
> units in the baseyear. In which model do you encounter these
> warnings?
>
> I tried to run eugene sample project for both estimation and
> simulation, and I didn't seem to get any of similar warnings.
>
> Liming.
>
> On Fri, May 2, 2008 at 11:07 AM, Brian Miles <Brian.Miles_at_uvm.edu>
> wrote:
>>
>> Hello,
>>
>> After recently upgrading to the latest development version of OPUS, I
>> noticed the following messages that appear when our location choice
>> models run:
>>
>> WARNING: Problem with sampling alternatives.
>> some values of rows [ 929 1797 2590 3657
>> 3757 5265 7923 10166 12310] in weight_array are less than 0
>>
>> The locations differ across models, and sometimes there are hundreds
>> reported in the message.
>>
>> I thought this was a strange message, so I decided to compare the
>> output of our model to the Eugene example. I found similar "errors"
>> in the Eugene model.
>>
>> My questions are: 1) what does this message mean; and 2) does it
>> indicate a problem that needs to be corrected?
>>
>> Thanks,
>>
>> Brian
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Received on Sun May 04 2008 - 13:46:13 PDT