I have tried to use this snippet of code
https://code.msdn.microsoft.com/windowsdesktop/Net-Implementation-of-a-d3ac7b9d
to implement a heap-based implementation of Prim's algorithm to solve the Minimum Spanning Tree (MST) problem in a non-directed connected graph.
after a few iterations, i find that the heap/priority queue is not well maintained anymore.
that is the head of the PriorityQueue doesn't have the lowest Key in the Heap.
PQ 0 [-7230, 309]
...
PQ 146 [-7277, 308]
Has anyone use this code and experienced similar problems ?
I can post a link on GitHub if anyone would be looking at it
My needs are for a heap datastructure which supports deletion of an element in the middle. It looks like Fsharpx.collections doesnt have such a data structure.
does anybody know a good implementation available somewhere ?
thanks
Recently, I ported a MaxHeap from PLINQ to F# here and made it MinHeap. It is array-based and performs much better than any "pure functional" alternative.
However, after a lot of benchmarking, I found that SortedDeque based on just a simple sorted circular buffer performs significantly better on most use cases even when I need to add or delete in the middle.
My answer is inspired by V.B. but here it is in full
I have used another library than FSharpx.collections, it is called
Spreads
read that page for details and instructions.
SortedDeque is the data structure i need for this problem.
I used the same code, just changing from the microsoft blog page code to the library functions and found the good result, so it is indeed some bug in the microsoft blog page code
PS. this spreads library has been designed to format financial data for quantitative analysis and i'm happy i found it !!! IT looks like this library is rather recent and thats why its not on top of Google's search or referenced in any other SO question (or if it is i didn't see it)
FSharpx.Collections is of no use for that problem as you can see from that discussion heap issue in FSharpx.Collections
Related
I want to simulate lidars. I saw that a class DepthSensor was mentioned in the documentation, but I have not found its actual implementation. For now, I am planning on using the RgbdSensor class and use only the height I need of the depth point cloud I receive to simulate my lidars.
Just to get your input on that, maybe I missed something, but is there a specific class for lidars, and how would you go about adding lidars to a simulation?
Thanks in advance,
Arnaud
You've discovered an anchronism in the code. There had previously been a lidar-like sensor (called DepthSensor). The extant documentation refers to that class. The class's removal should've been accompanied by a clean up of the documentation.
The approach you are taking is the expected approach given Drake's current state.
There has always been an intention to re-introduce a lidar-like sensor in Drake's current architecture. It simply hasn't been a high priority.
I'd recommend you proceed with what you're currently doing (lidar from depth images) but, at the same time, post an issue requesting a lidar-like query with specific focus on the minimum lidar-properties that you require. A discussion regarding how that would differ from what you can actually get from the depth images would better inform of us your unique needs and how to prioritize it. (You can also indicate more advanced features that you need less but would be good to have, of course).
As for the question: how would you go about adding lidars?
That's problematic. Ideally, what you would need is ray-casting ability. The intent is for QueryObject to support such a query, but it hasn't happened yet. (It's certainly the underlying technology we'd have used to implement a LidarSensor.) In the absence of that kind of functionality, you'd essentially have to do it yourself in the most horrible, tedious way imaginable. I'd go so far as to suggest that it's not feasible with the current API.
I have tried to implement the ellipse fitting algorithm descibed in the following paper: “ElliFit: An unconstrained, non-iterative, least squares
based geometric ellipse fitting method”, by Prasad, Leung, Quek. A free version can be downloaded online from http://azadproject.ir/wp-content/uploads/2014/07/2013-ElliFit-A-non-constrainednon-iterative-least-squares-based-geometric-Ellipse-Fitting-method.pdf
The authors did not provide any publicly available implementation.
I have implemented the algorithm in Mathematica, I believe I have implemented it correctly, yet it fails to correctly find the fit parameters. The PDF of the experiment can be downloaded here: http://zvrba.net/downloads/ElliFit-fail-example.pdf
Did somebody else try to implement this particular algorithm and, if yes, what is the key to get it working? Is there a "bug" in the paper? Can somebody take another look at my implementation and see whether there's a bug there?
I know it's been almost a year since this question, but it seems that the authors have now provided public source code for ElliFit, both a MATLAB version and an OpenCV version.
Both are available on the the author's homepage. In case the homepage goes offline for some reason, both source codes are shared on Google and are available here (MATLAB) and here (OpenCV).
At the time of writing, I have not personally tested their code, but am planning to use them for a project. I will post any updates here in the next few days.
EDIT:
I got around to test the code sooner than I expected. I gave the OpenCV code a try. It works pretty well, as demonstrated by the image below (ignore the "almost-closed-ellipses". It's an artifact caused by something else in my code).
As you can see, it works pretty well, most of the times. There are some failure cases too (the small ellipse on the spray bottle next to the cup).
TraceGL is a pretty neat project that allows JS programmers to trace code paths in Javascript. It looks something like this:
I'd like to build something similar for Objective C. I know the runtime has made it rather easy to trace method calls, but how would I trace control flow? For example, in the screenshot above, code paths not executed are made obvious with a red highlight. What would be the best way to achieve something similar in an Objective C/Xcode workflow?
The best I've come up with so far is to write a preprocessor that injects code into temporary source files before sending them to the compiler. Anyone have a better idea?
I guess the visualizer for issues found by Xcode's static analyzer comes pretty close to this - albeit this one will only give you the call path for a particular issue like a memory leak.
Try "Product > Analyze" in Xcode, select any of the issues found on any given project and click on the blue arrow in the code editor to see for yourself.
Not exactly answer for Objective C and XCode.
For C++ code there is a industrial quality code coverage tool BullseyeCoverage
Function coverage gives you a quick overview and condition/decision coverage gives you high precision
Works with everything you can write in C++ and C, including system-level and kernel mode
If you want to invent/write this kind of tool yourself I'd recommend to take a look at (evaluate) some existing tools that solve the same task so that you don't miss a key functionality
There are basically 2 categories of such tools
working at binary level, instrument byte code, library entry points etc.
working at source level, instrument source code before going to the compiler
The purpose of the instrumentation is to insert into the code calls to a profiling runtime that collects the runtime statistics for further processing.
Basic calls
timestamp, thread id, source code address, entering
timestamp, thread id, source code address, leaving
The source code address depends on the granularity you are interesetd in. It can be a function name ot it can be a source file and line number.
Collected performance data can be quite huge so they are usually summed-up and whole callstacks are not captured. It is usually sufficient level of detail for detecting performance bottlenecks.
Another drawback is that capturing detailed performance data especially in code points with many hits will slow the application significantly.
If you want complete history then capture the full trace including timestamps and thread-ids and you will be able to recreate the call stacks later knowing that each enter has corresponding leave.
To guarantee this pairing the code instrumentation must insert exception handling calls to make sure that exit point will be logged even if the function throws an exception (what is the "exception" and how to try-finally it dependes on the language and the OS platform).
To get all necessary tricks and tips evaluate some tools and take a look at their instrumentation style.
BTW: in general it is quite a lot of work to do and to get right I'd personally thought twice or more times about what will be the outcome and what will be the costs.
As a want-to-play-with topic I fully recommend that. I created such a tool for troubleshooting Java MIDP applications working at C++ source level and Java binary level and it was helpful at the time when we needed it.
Does it happen that no one ever needs histogram in Delphi ?
Google gave me a bunch of half-baked code snippets. But it means that each time you need one - you have to invent one more ad hoc bycicle.
Torry mostly told me about some very expensive closed source Math Statistics or Financial packages, that as a subproduct have histograms. But they are very expensive and since you have no source code, each time you install update onto IDE/RTL/VCL you're probably screwed, until the vendor would make (soon ? ever?) updated packages. Given thatvendor is still does exists.
S.O. told me nothing, nil.
For what i found...
Mitov.com provides some histograms in PlotLab. which told to be free for non-commercial. Alas, it is again closed-source, and if the Histogram - quite fancy let's admit -is the onlything i need from it - why pay the whole price ?
One more example http://DSpatial.sf.net
Just few years ago i used it in Delphi 5, but even then i felt the author is loosing interest in the project. I made few enhancement, fixed some bugs, he merged them and that's all. The component was not very useful and lacked upon features, yet better than nothing. Now the project seems to be completely dead. Good old days, etc. But i do not want them back :-)
And Stack Overflow seemingly carries no single question about it. But maybe just no one bothered to create topic, after search found nothing ? I mean, Delphi was created for database access, histograms are one of basic ways to visualize data, and no one crosses them ? Something with nice style, with rich mouse tooltip like in HTML/CSS/JS on http://www.moskva.fm/stations/FM_95.2 ?
Or is this too domain-related and not ever possible to have good abstraction ?
TChart is a control that ships with most versions of Delphi. TChart can be used to make histograms (bar charts) in style. The following give you some ideas about how to use it: http://www.digitalcoding.com/tutorials/delphi/Simple-steps-to-create-Delphi-chart.html and http://delphi.about.com/od/adptips2006/qt/chart_selectbar.htm .
If you need something with code, google the pages at delphiforfun.org/programs/oscilloscope.htm . These are not controls. The oscilloscope article has a histogram with source. Some of the other projects at the site have other histogram graphs with source..not elegant but useful and free. Use them as a template to make your own control.
The link at http://delphiforfun.org/programs/Math_Topics/probability_distributions.htm shows how to make your own statistics displays with "histograms." This example makes use of TChart.
Here is some more stuff to try I found looking at my resource file:
http://wiki.lazarus.freepascal.org/TAChart, http://members.home.nl/mvanwesten/en_lazarus.html , http://www.martinole.org/TAChart.html ...some of these are GPU components that supposedly work with some versions of Delphi. Perhaps this is your lucky day as there is some source code. The first and third listed probably will work reasonably for histograms. You may have to write your own statistics algorithms.
Found this thread while doing some searching. The ImageEn component suite has a THistogramBox component. It's the NOT prettiest thing in the world, but it's the only one I've found so far.
http://www.imageen.com
I came across a histogram example in a gdiplus package available for download from code central. I don't know if it will do what you need but when I saw it I remembered your SO question.
HTH.
If you were using firemonkey, you could just created a series of TRectangles in series. They can be made unclickable by turning hittest off. Or is that too easy and straightforward?
I'm looking at the excellent dwscript for Delphi see here which provides a useful set of classes to implement a built in pascal script for your Application. I would very much appreciate some help with an example of how to link together the supplied debugging interface with an editor so that I can create breakpoints (and ideally see watches). Has anyone gone along this route please?
Thanks,
Brian
Most of the debugger doc is currently in this post
http://delphitools.info/2010/12/03/spotlight-on-dwss-idebugger/
Also the debugger interface hasn't changed much (if at all) since the original DWScript II (on SourceForge), so the old demos there should hopefully still work with minimal adjustments.
http://sourceforge.net/projects/dws/
For breakpoints, you basically just check the source position of the Expr you get in DoDebug/OnDebug against the list of breakpoints. One simple and efficient way is to merely use TBits -using it as a boolean array of which lines have a breakpoint).
Evaluating/watching requires looking up a symbol, which will give you it's stack address, you can then lookup the value in the stack.
I'll try to add/update a debugging tasks demo for v2.2 (unless someone else does it before me ;) )
edit: as of 11-02-14 there is a TdwsDebugger component to facilitate debugging tasks.