I have looked for solutions but their all either too complex of will take too long. Is there a simple way to fix this?
Related
I asked this on the soplex mailing list, but no answer yet:
http://listserv.zib.de/pipermail/soplex/2022-August/000001.html
I tried scip, and it took 30sec. Maybe because it performs pre-solve.
Is there an easy way to achieve my objective:
Specify an initial solution (something that I have, which is better than a random init), and use the solver for a limited time to find a better feasible solution
https://math.stackexchange.com/questions/4510587/find-a-feasible-but-not-optimal-solution-to-a-large-lp
Reply from the mailing list:
http://listserv.zib.de/pipermail/soplex/2022-August/000002.html
To find only a feasible solution, you can just remove the objective function. This will terminate as soon as feasibility is attained. Then, you could plug in this solution as a starting basis - I don't think this is going to help much, though.
I am using PySCIPOpt and have a MIP with some quadratic constraints (works). Now, I want to implement a Primal Heuristic (should run once before presolving), that fixes certain Variables and optimizes afterwards.
Ìn pseudo-code something like:
For x in ToFIX:
model.fixVar(x, my_guess(x))
model.optimize()
*Any found solution is used as solution of the original problem*
For x in ToFIX:
model.unFixVar(x)
I worked around that problem by creating a second model, solving that, identifying the variables by their name and using model.trySol().
This mostly works but is slow and certainly not the way it is meant to be implemented.
Any hint, which functionalities to use is appreciated.
sorry this took a while to answer.
What you want to implement is a sub-scip heuristic. This is certainly possible, but if you want to do it in PySCIPOpt you might have to wrap some missing methods from the C-API.
I suggest you take a look at heur_rens.c in the SCIP code. The methods you would need to wrap are probably SCIPcopyLargeNeighborhoodSearch and SCIPtranslateSubSol which should save you a lot of trouble. Please refer to the section extending the interface in the PySCIPopt Readme.
I have a enum based and complicated structure. I want to change my structure with object oriented structure. You must know this there are too much states. So I searched in Internet and I found solutions like that
http://blogs.microsoft.co.il/gilf/2009/11/22/applying-strategy-pattern-instead-of-using-switch-statements/,
Ways to eliminate switch in code .
When I apply this solutions, there will be too much classes. What do you think about it, Should I apply like that.
Yes, definitely. You should go for the Strategy solution.
And in my experience, there is almost never a case of too much classes, as you put it. On the contrary, the more modular your code is, the easier it is to test/maintain/deploy it.
You'll run a lot in the opposite problem: a class you thought is small enough and there will be no reason to change, and then after a change in the requirements or a refactoring you see that you need to make it more modular.
I'm currently taking part in a "Data modeling" course. And for my final project, I need to make a research about "R-tree index for spatial searching". However, I'm not at all familiar with many concepts concerning the subject matter (spatial data, multi-dimentional data,...).So, I read the wiki and as I encountered new concepts, I tried to learn them on the way.
However, I don't think this top-down approach is a very efficient way to go about this. Thus, I'd really appreciate it if anybody can suggest a way/lists of things that I need to read up in advance, in order to understand R-tree, and hopefully make some kind of implementation out of it.
Start with the original paper and check out (shameless self promotion) a basic R-Tree implementation in Java.
In Processing.js, I'd like to have circles that represent nodes, with lines connecting linked nodes. I'd like those connected circles to naturally pull toward each other with a kind of elasticity of the lines, and the circles to bounce against each other when they touch. Any ideas on how to do this?
I think this sample might get you going in the right direction:
Box2D.JS with Processing.js
It has the circles, the lines, and the bouncing.
Or if you want it yourself this is the Google search term you're looking for:
http://www.google.com/search?hl=en&q=force+directed+graph+javascript&aq=f&aqi=g-c1&aql=&oq=&gs_rfai=
The base algorithm is pretty simple, getting a tuned example to work a little less so. I've looked through this stuff before, but this quick search just turned up this little js project that seems to do it quite properly: http://github.com/jackrusher/jssvggraph
Shouldn't be too difficult to port.