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Sidd
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Message 63771 - Posted: 25 Jun 2015, 16:28:41 UTC

Hey All,

Just a quick update on the status of Nbody. I discovered that the hanging that people were experiencing were due to the Newton Raphson root finding algorithm which would get stuck in an infinite loop. After looking for why this occurred for sometime, I decided to switch to a bisection method which is insured not to get stuck.

The slow nature of the initialization of the plummer was found to be an error in the calculation of one of the limits of integration in a crucial integral that was being calculated. What a time it was finding that! With that limit fixed, it seems that the initialization takes a few seconds!

I am currently unit testing the code and hopefully should get a lovely new version in a couple of weeks.

Cheers,
Sidd

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Message 63788 - Posted: 7 Jul 2015, 10:20:06 UTC

Thanks for the update Sidd.
Looking forward to reactivating N Body simulations once you give the word.

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Message 63794 - Posted: 11 Jul 2015, 21:32:57 UTC

Thanx for the update, Sidd!

I am also looking forward to allowing the NBody on my PCs.
It is my absolutely favourite multi-threaded app of all times - of all the projects of distributed computing!
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Message 63797 - Posted: 13 Jul 2015, 14:48:03 UTC

Hello Sid,
Great detective work. However, I might have a "heads up" for you to think about. Microsoft is planting Version 10 on PCs round the world in waves starting sometime around August 2015. I am fairly sure that folks running Windows 8 will gladly update to get rid of the painful "anomalies" in version 8 and 8.1. Eventually, Windows 7 users will convert to 10 once they see that version 10 is reliable. This migration is bound to affect grid computing projects.

I do not know if Windows 10 will require new driver upgrades for chipsets and other motherboard internals, but you may want to consider that a scary thought. Microsoft is not talking about it, even when asked. If you have connections, ask. It might affect your code.

Windows anything causes weird stuff to happen with multithreaded apps because it causes timing issues. Watch your back.
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Sidd
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Message 63800 - Posted: 14 Jul 2015, 16:32:12 UTC - in response to Message 63797.

Hey,

Thanks a ton! Yep, I can tell you we are definitely concerned. But most likely we will have to wait and see. The actual code itself should still work, its all the other things, like compiling and getting it running on client computers, that may be affected. But as it is, we use an windows XP machine to compile our code for windows which allows for a wider range of volunteer machine use. Hopefully, things will still be compatible. But, again, we will have to wait and see.


Cheers,
Sidd

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Message 63845 - Posted: 31 Jul 2015, 20:20:10 UTC - in response to Message 63800.

You mentioned about compiling nbody on an XP machine. Last I recalled, XP was only 32 bit. You seem to be doing a lot of floating point arithmetic. Are you doing double-precision? If so, wouldn't a 64-bit compiled version have to use different code and at least a 64-bit compiler? Am I missing something?
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Message 63848 - Posted: 3 Aug 2015, 11:40:37 UTC - in response to Message 63845.

You mentioned about compiling nbody on an XP machine. Last I recalled, XP was only 32 bit. You seem to be doing a lot of floating point arithmetic. Are you doing double-precision? If so, wouldn't a 64-bit compiled version have to use different code and at least a 64-bit compiler? Am I missing something?


I understood that Windows XP came in both 32 and 64 Bit flavours, not just 32 Bit.
But as Sidd took down the Windows app for N-Body due to a bug that appears to yet be fixed then this is probably a mute point.

I just came back to run a few N-Body work units on my Linux computers, but as none are currently available I will have to wait.

Conan
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Message 63861 - Posted: 9 Aug 2015, 6:51:23 UTC

Hey Sidd, can we get a possible ETA on the new N-body being ready?

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Message 63862 - Posted: 10 Aug 2015, 3:36:36 UTC
Last modified: 10 Aug 2015, 14:06:39 UTC

Hey Captiosus and Everyone Else,

I might be able to help you with an answer to your question. So lets go over a quick run down of what has happened with N-body over the last month and a half or so:

1. The bugs Sidd mentioned in this thread have been fixed.
2. As always fixing one bug reveals there are more bugs hidden throughout the code (Sidd wrote this entire initialization procedure from scratch trying to optimize for efficiency and make it long term maintainable. (Well actually I helped a little with the optimizing but it his baby.) He had to start from scratch because this is a very rarely used, complex, and interesting distribution we using to improve the accuracy of our simulations.) and he recently found that the required time step for an accurate simulation was being calculated incorrectly.
3. Luckily fixing the bug found in part two was really easy and is done now.
4. Now Sidd is just doing some last testing on the code to make sure all of the previously mentioned bugs are gone for good. He is also making sure that the distributions we are creating really are correct and everything is working as intended.

So to answer your question, Sidd should be releasing a new version of N-body very soon. If you are interested in keeping up with his changes in real time, feel free to check out our github repository and you can see how much work he is putting into this. Also take everything I say with a grain of salt because I am not actually Sidd and I am just an outsider checking in with his side of the project every now and again (but I see him in person so even when he is super engulfed in his work he can't forget to answer me).

I will continue to bug Sidd about making more dev blog posts so you all can keep up with the going on with N-body as he is working on it.

Happy Crunching,

Not-Sidd

(a.k.a. Jake W)


[Edit]

Maybe I can get Sidd to post some videos of our distributions floating around being stable. That would be really cool.

[/Edit]

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Message 63863 - Posted: 10 Aug 2015, 8:33:13 UTC

Groovy. Looking forward to it.

Sidd
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Message 63872 - Posted: 12 Aug 2015, 18:33:10 UTC

Hey All,

I just posted a new blog post. Check it out:

http://milkyway.cs.rpi.edu/milkyway/forum_thread.php?id=3798

Cheers,
Sidd


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