Wikipedia:Reference desk/Archives/Computing/2014 October 24

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October 24

Windows Explorer List Order

I'm using Windows 7. When I copy and paste files from one Windows Explorer folder to another, they get added at the bottom of the list, not alphabetically, even though the window is sorted on the Name column. I then have to refresh the window before they pop into place.

Is there a configuration option that will force Windows to drop new files in at the right place?

Thanks, Rojomoke (talk) 13:10, 24 October 2014 (UTC)

Advanced histogram plot

I am plotting a function, from reals to reals, that is a sum of a finite number of dirac delta functions. I need to plot it like a histogram, with the area of each bar proportional to the area under the corresponding delta function, and the width of the bar the maximum possible so as to avoid overlap with the neighboring delta function.

I'm using Octave on Linux. Can anyone suggest plotting software, or code that will do what I want? Thanks! --RM — Preceding unsigned comment added by 121.247.216.109 (talk) 15:47, 24 October 2014 (UTC)

Octave produces histographs. Example: hist (randn (10000, 1), 30); — Preceding unsigned comment added by 209.149.113.162 (talk) 18:32, 24 October 2014 (UTC)

Last I used Octave, it had to hook into gnuplot to do that sort of thing, and that could be a bit tricky on some installations. But if OP can get Octave to plot anything directly, then 'hist' will indeed plot a histogram [1]. SemanticMantis (talk) 20:58, 24 October 2014 (UTC)

Wait, the area under Dirac_delta_function is 1 for any interval that contains the center point, right? Are you thinking of something like a Dirac comb, but with some sort of weighting? I would suggest doing whatever manipulations you want to get the appropriate heights and widths, then just feed that vector to 'bar' or similar, rather than trying to get a plotting command to correctly interpret the deltas. SemanticMantis (talk) 21:04, 24 October 2014 (UTC)

The function is a sum of a finite number of weighted shifted dirac delta functions.

The "boxes" style in Gnuplot seems best as of now. Is there any plotting program that allows individual bar width to be adjusted for histogram plots? --RM — Preceding unsigned comment added by 121.247.216.109 (talk) 22:43, 24 October 2014 (UTC)

boxes does let you set each width—it even can compute it to touch like you want, but you still need them yourself to compute the correct heights. --Tardis (talk) 00:26, 25 October 2014 (UTC)

BeagleBoard: making it mobile

If you buy a BeagleBoard, can you make it mobile attaching a battery and a screen to it? And what battery and screen would be a choice? I'd like the less colorful screen (but still touch screen) and the bigger battery (think: less esthetically minded, prefer longer running time). — Preceding unsigned comment added by 217.12.24.130 (talk) 17:51, 24 October 2014 (UTC)

Yes, it is possible. Review the latest BeagleBoard System Reference Manual. There is a whole chapter on power supply systems.

If you provide 5 volt DC power, you can expect that the supply will need to source around a half an ampere. (The spec actually says 1.5 A minimum). Not all batteries can do that safely. Choose wisely!

In other words some batteries will fail gracefully, (i.e., your board will suffer a brownout). (This is a more likely scenario for most of the kinds of batteries that are within the price-range of the enthusiast/hobbyist). But if you decide to shell out big bucks for bigger batteries with longer lifetimes, you need to be aware: some batteries will leak chemical, catch fire, or explode, if you sink too much current out of them. Some (bigger) batteries will over-current the Beagle Board and blow out its overcurrent protection circuit.

The moral of this story : before you go connecting a yacht-sized marine battery to your computer, you should read up on DC-DC power supply design. Choose an appropriate energy source (battery); choose an appropriate DC voltage and current regulator; choose appropriate cables and protection circuitry. If you do it all correctly, you can hook up a yacht battery, and you can run the board for days, hours, weeks or months. I once worked on a project where we hooked up many dozen (about a metric ton) of marine batteries to a small embedded system... its computer system and radio uplinks survived for several years until "a shark ate it." Nimur (talk) 18:22, 24 October 2014 (UTC)

Are you really set on using a BeagleBoard? Those things are like 5 or 6 years old - a BeagleBone Black would be a more reasonable choice...and it's significantly smaller. If only needs 460 milliAmps at 5 volts - and then only when everything is running. Most of the time it's more like 250mA. Four rechargeable 2900mAh Nimh AA batteries would get you plenty of battery life. This display plugs directly into the BeagleBone and has an integrated touch screen...not sure how much power it'll consume though. SteveBaker (talk) 19:19, 24 October 2014 (UTC)

Thanks for the tips. Yes, I'd go with the BeagleBone and not the original BeagleBoard. And go with some kind of replaceable, small battery. I'll try to find one specific to the BeagleBone, since it looks they are developing components specific to it. — Preceding unsigned comment added by 87.222.207.165 (talk) 18:06, 25 October 2014 (UTC)

Yeah - I'm sure someone has already done exactly what you need. I've been using BeagleBones for quite a while now - they are a great platform for this kind of thing. I have one driving my $10,000 laser cutter! SteveBaker (talk) 22:45, 25 October 2014 (UTC)