I'm trying to use Optaplanner to implement the "VRPP" variation, where all customers don't need to be delivered to.
It seems like the example code I'm use for time windowed VRP ensures that all customers are in the "chain". I want to make that optional and then add to the score if they are in the chain. (If the "profit" of visiting them improves the score more than the cost they would be in the chain.)
I had assumed the problem was initialized with a complete chain and then moves only swapped positions, but I can't where or if that is happening.
Has someone implemented VRPP with optaplanner?
Read overcontrained planning in the docs, this about not having to assign all assignments.
Normally, you would be able to use nullable=true, but the new #PlanningListVariable doesn't support that yet, and neither do the old #PlanningVariable(CHAINED) (only if chained).
Introduce a dummy vehicle (with a field boolean dummy = true). Ignore the dummy vehicle for all hard and soft constraints. Use HardMediumSoftScore. Add a medium constraint to penalize all dummy vehicle assignments. Or instead add a medium/soft constraint summing the profit per assigned customer.
Related
I am trying to work with Optaplanner in order to solve the following simple exmample :
https://www.gams.com/products/gams/gams-language/#the-gams-language-at-a-glance/
simple inventory allocation exemple
I find it very difficult to do so since I couldn't find a similar cas on optaplanner
Can anyone help ? some directions, ressources
thanks in advance
It looks like the Facility Location Problem in OptaPlanner Quickstarts, but a consumer can pull from 2 or more suppliers at the same time.
Because the number of units to ship from supplier A to consumer X is an integer (*), you would need to use continuous value ranges and custom moves like in the investment example. Not simple (unlike other use cases in OptaPlanner), but doable.
(*) These business requirements are maybe unrealistic: in the real world, a half-full truck is almost as expensive as a full truck.
This is a fundamental application design question I’ve struggled with and flip-flopped on for years. We have a legacy webapp that doesn't really have a solid ORM, if that tidbit might influence your answer. To abstract my question let’s say we have a class Car, and a corresponding table in our database named car. Car has a few properties: color, weight, year, maxspeed These properties directly correspond to columns in the db table.
In our application, we define the car as “classic old” if year is < 1960 and color = black. And in many places within our app knowing whether the car is "classic old" is extremely important (maybe we’re running a very illogical insurance agency which gives steep discounts and other perks to cars which are “classic old”).
All over our application, we do things like:
--list all classic old cars
--give the current user a discount if their car is classic old
--list all classic old cars with max speed > 100 miles per hour
--email the current user if their car is classic old and weights more than 1000 pounds
What is the best way to go about this? We have a legacy application that does this in some places:
getOldClassicCars()
select * where year < 1960 and color = black
and in other places:
cararray = getAllCars();
for each car in cararray
if car.year < 1960 and car.color = black
oldcararray = car.add()
The point being that this very important, fundamental piece of our application – is the car classic old – is “hardcoded” as year < 1960 and color = black in many places. Sometimes in SQL, sometimes in application code, etc. Obviously that is not good, but as we’ve refactored things I’m not sure we’re refactoring things the best way we can.
Well, you are stuck with the fundamental problem that
you cant run your code on the database
you want to be able to use the database's selection functionality on this criteria.
you want the calculation of "classic old" to be defined in a single place (preferably code)
Lets enumerate the solutions
1: Put the calculation in a sproc and always use the sproc to retrieve cars.
The problem here is if you create a new car in code, its class status is undefined, so you haven't really solved the 'not in two places' problem.
2: Get the DB to run your calc via an assembly. for example you can get mssql to run functions from a .net assembly which you can also use in your code base to perform the same calculation.
Problem, its hard work. Plus essentially its still in two places, you have to keep the db up to date and ensure that the table is accessed correctly
3: Persist the calculated value on the DB, but perform the calc in the code
Problem, if the calculation changes the DB values will be incorrect and need updating.
3 seems to be the best option, as we will know when the calculation changes and be able to take some action to resolve the situation.
However, it might be best, given the fundamental nature of this calculation, to make that 'out of dateness' implicit in the way we structure the code.
Instead of simply persisting car.IsClassic we could add a CarStatusReport object with a datetime property. We then generate a CarStatusReport(2017) which evaluates all the cars at that point in time and saves that data in a separate table.
Our business logic is then no longer, "Is this car a classic?" but "What does the latest CarStatusReport say the status of this car is?"
You Business Logic will then reside in a single CarStatusReportGenerator service and any other logic accessing the IsClassic calculation, will be forced to acknowledge the ephemeral nature of the stored info.
No optimal solution here. But, one good point will be to move all the business logic into the one place. If you can't (when you make methods or functions calculating some property, for example isOld()) then hide all those inconsistencies under the hood, so implementation users (conceptually) will never notice DRY violation from outside.
Is it Possible to optimise the VRPTW by using only one vehicle.Since the single vehicle must go to the customer in sequence of the appointment time of customers.
Yes, it is. In the VRPTW example, simply add only 1 Vehicle instance in the Solution's vehicleList.
Academically, that's more a TSP(TW) than a VRP(TW) though.
I successfully amended the nice CloudBalancing example to include the fact that I may only have a limited number of computers open at any given time (thanx optaplanner team - easy to do). I believe this is referred to as a bounded-space problem. It works dandy.
The processes come in groupwise, say 20 processes in a given order per group. I would like to amend the example to have optaplanner also change the order of these groups (not the processes within one group). I have therefore added a class ProcessGroup in the domain with a member List<Process>, the instances of ProcessGroup being stored in a List<ProcessGroup>. The desired optimisation would shuffle the members of this List, causing the instances of ProcessGroup to be placed at different indices of the List List<ProcessGroup>. The index of ProcessGroup should be ProcessGroup.index.
The documentation states that "if in doubt, the planning entity is the many side of the many-to-one relationsship." This would mean that ProcessGroup is the planning entity, the member index being a planning variable, getting assigned to (hopefully) different integers. After every new assignment of indices, I would have to resort the list List<ProcessGroup in ascending order of ProcessGroup.index. This seems very odd and cumbersome. Any better ideas?
Thank you in advance!
Philip.
The current design has a few disadvantages:
It requires 2 (genuine) entity classes (each with 1 planning variable): probably increases search space (= longer to solve, more difficult to find a good or even feasible solution) + it increases configuration complexity. Don't use multiple genuine entity classes if you can avoid it reasonably.
That Integer variable of GroupProcess need to be all different and somehow sequential. That smelled like a chained planning variable (see docs about chained variables and Vehicle Routing example), in which case the entire problem could be represented as a simple VRP with just 1 variable, but does that really apply here?
Train of thought: there's something off in this model:
ProcessGroup has in Integer variable: What does that Integer represent? Shouldn't that Integer variable be on Process instead? Are you ordering Processes or ProcessGroups? If it should be on Process instead, then both Process's variables can be replaced by a chained variable (like VRP) which will be far more efficient.
ProcessGroup has a list of Processes, but that a problem property: which means it doesn't change during planning. I suspect that's correct for your use case, but do assert it.
If none of the reasoning above applies (which would surprise me) than the original model might be valid nonetheless :)
What I want to do is implement submission scoring for a site with users voting on the content, much like in e.g. reddit (see the 'hot' function in http://code.reddit.com/browser/sql/functions.sql). Edit: Ultimately I want to be able to retrieve an arbitrarily filtered list of arbitrary length of submissions ranked according to their score.
My submission model currently keeps track of up and down vote totals. Currently, when a user votes I create and save a related Vote object and then use F() expressions to update the Submission object's voting totals. The problem is that I want to update the score for the submission at the same time, but F() expressions are limited to only simple operations (it's missing support for log(), date_part(), sign() etc.)
From my limited experience with Django I can see 5 options here:
extend F() somehow (haven't looked at the code yet) to support the missing SQL functions; this is my preferred option and seems to fit within the Django framework the best
define a scoring function (much like reddit's 'hot' function) in my database, and have Django use the value of that function for the value of the score field; as far as I can tell, #2 is not possible
wrap my two step voting process in a suitably isolated transaction so that I can calculate the voting totals in Python and then update the Submission's voting totals without fear that another vote against the submission could be added/changed in the meantime; I'm hesitant to take this route because it seems overly complex - what is a "suitably isolated transaction" in this case anyway?
use raw SQL; I would prefer to avoid this entirely -- what's the point of an ORM if I have to revert to SQL for such a common use case as this! (Note that this coming from somebody who loves sprocs, but is using Django for ease of development.)
(edit: added this after further discussion) compute the score using an extra select parameter containing a call to my function; this would work but impose unnecessary load on the DB (would be forced to calculate the score for every submission ever made every time the query ran; caching could help here, but it still seems like a bit of lame workaround)
Before I embark on this mission to extend F() (which I'm not sure is even possible), am I about to reinvent the wheel? Is there a more standard way to do this? It seems like such a common use case and yet in an hour of searching I have yet to find a common solution...
EDIT: There is another option: set the default value of the field in the database script to be an expression containing my function. This is not as flexible as #1, but probably the quickest and cleanest approach to solving the problem (although my initial investigation into extending F() looks promising).
Why can't you just denormalize the score and reconstruct it with the Vote objects every once and a while?
If you can't do that, it is very easy to make a 'property' function that acts as an object attribute for scoring.
#property
def score(self):
... calculate score from Vote objects ...
return score
I've never used F() on a property like this, but it's Python, so I bet it works.
If you are using django-voting (which I recommend), you can put #3 in the manager's record_vote function since that's how all vote transactions take place.