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I'm looking at a physical problem on an hexagonal 2d lattice. It's now a geometrical problem, only a subset of the edges of the lattice are of interest, I'm given this set. I should then restrict myself to the closed curves that I can compose with these edges. From these polygons I'd like to extract information such as their diameters (maximal distance between two of its points)) and their fractal dimension.
I still don't see how to it from the raw initial data (unordered array of edges) and so I'd like to know if there are packages/library that could help me. From drawing each one of these edges they could return the closed loops they form and after that, analyzing each of these polygons individually.
Thank you.
You can use the box-counting algorithm to compute the fractal dimension:http://en.m.wikipedia.org/wiki/Minkowski%E2%80%93Bouligand_dimension.
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So i've been struggling to find code which can solve a set of simultaneous equations and also handle possibilities of Infinite Solutions, i.e. a singular Matrix. From all the sample code Gaussian Elimination in C that i've encountered the problem arises when dividing by zero in one of the steps for row reduction. Surely there must be some numerical ways to counter this problem.
Gaussian elimination[1] does not work on singular matrices. As you noticed numerically this usually leads to devision by zero or some other problem. If you suspect that a the matrix you want to diagonalize might be singular (or numerically close to singular) you should check out Singular Value Decomposition (SVD) which either provides you with the inverse matrix or something close. A nice resource is Numerical Recipes[1] or GSL[2] if you want to look into the how and why.
[1] http://www.haoli.org/nr/bookcpdf.html (Chap. 2.1)
[2] http://www.gnu.org/software/gsl/
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I've recently begun development on a project that requires me to visualize graphs, and I am looking for a decent algorithm to tackle this problem.
The graphs I'm drawing model data flow, so a reasonable drawing could be left-to-right or top-to-bottom. They are, of course, directed and mostly acyclic -- that is, there might be a few backwards edges, but these would be a small proportion and I would be happy to remove these before calculating vertex positions if having a DAG as input would substantially improve runtime.
I'm using C++ and Qt for this project and am already very familiar with the Elastic Nodes and the Diagram Scene examples Qt provides. If anyone has seen KCacheGrind, what I'm trying to do is similar to its call graph visualization.
My current attempts have included an original algorithm that assigns each node to a layer based on its minimum distance from the root and then tries to position the nodes inside each layer in such a way that edge crossings are minimized. I was unable to implement the last part of that correctly, and I believe the problem to be NP-Hard.
What I'm looking for is guidance as to what kinds of algorithms have been used to efficiently solve this problem in the past.
I'd suggest using QGraphicsScene to implement directed acyclic graph. Also please check these links to help you out with implementation:
https://github.com/qknight/automate
http://invalidmagic.wordpress.com/2009/12/10/qgraphicsscene-used-as-a-qabstractitemmodel/
http://socnetv.sourceforge.net/
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I am looking for the best package for sparse matrix multiplication on single core solution.
I am not looking for CUDA, MPI or OpenMP solutions.
My preference for languages in decreasing order : Matlab, Python, C/C++.
Matlab has its own matrix multiplication function which can be used for sparse matrix multiplication. But are there any better package(s) available ?
I have to multiply two large matrices which are in sparse format.
Eg., one matrix is 677000-by-48000 and another is 48000-by-8192. Here, n-by-d means n : # of rows, d : # of columns
I'm no expert for sparse matrices but I do know the renowned 'eigen' C++ library.
They have a tutorial on sparse matrices, reachable from the documentation page.
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Are there any good Webservices apart from Google one which can find me the distance between two Zip Codes?
I have
http://maps.googleapis.com/maps/api/distancematrix/json?origins=95050&destinations=94087&mode=bicycling&sensor=false
which is Google API. Are there any other API's that I can take a look? If yes, can anyone provide me the link for the same?
There is a very simple API that will calculate distance between two zip codes. There are also options for zipcodes within a radius and finding the lat/long and city/state. http://zipcodedistanceapi.redline13.com/
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I need something alike CGAL gives in terms of simple boolean operations on top of 3d meshes but in lib Bullet. So I wonder if there is 3D Boolean Operations on meshes in Bullet? (cant find any dedicated chapter in manual, am I blind?)