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by ejolson
Fri May 25, 2018 4:51 am
Forum: General discussion
Topic: Release: Multiple 64Bit OS 3bplus desktop&lite
Replies: 17
Views: 805

Re: Release: Raspbian 64bit desktop

ShiftPlusOne wrote:
Tue Apr 17, 2018 5:52 pm
it does seem to be 32 bit Raspbian with a 64 bit kernel.
Does Mathematica still work under the 64-bit kernel?
by ejolson
Fri May 25, 2018 4:39 am
Forum: Gentoo
Topic: How to install and run 32-bit Raspbian apps on 64-bit Gentoo (RPi3 B/B+)
Replies: 1
Views: 149

Re: How to install and run 32-bit Raspbian apps on 64-bit Gentoo (RPi3 B/B+)

sakaki wrote:
Tue Apr 17, 2018 7:00 pm
you may sometimes find yourself wishing you could just install and run a particular 32-bit package from Raspbian, if it has not yet been added to the Gentoo arm64 tree.
Does the 32-bit version of Mathematica included free with Raspbian work?
by ejolson
Thu May 24, 2018 4:59 am
Forum: C/C++
Topic: Odd happenings at 32 and 64 bits
Replies: 29
Views: 442

Re: Odd happenings at 32 and 64 bits

jahboater wrote:
Wed May 23, 2018 10:48 pm
The C17 standard says: "Exact-width integer types" and various "Minimum-width integer types" of which we are talking about:-
How do you print exact and minimum width integers? Does C17 specify corresponding exact and minimum width format specifiers for use with printf?
by ejolson
Wed May 23, 2018 5:58 pm
Forum: Teaching and learning resources
Topic: Non-internet-connected wireless server...?
Replies: 2
Views: 572

Re: Non-internet-connected wireless server...?

Arushi wrote:
Wed May 23, 2018 4:35 am
I have done it
Me too. Make sure to disable power saving on the Pi WiFi or your access point might disappear.
by ejolson
Wed May 23, 2018 2:28 am
Forum: Mathematica
Topic: [Question] Perimeter
Replies: 11
Views: 245

Re: [Question] Perimeter

One might also want to look at the Coastline paradox . It might not be as simple as some think. Interesting article. While the length of the coastline may not be well defined, the area enclosed is. But now that I reread the question I see that it isn't a matter of finding the area, but whether a pa...
by ejolson
Tue May 22, 2018 10:13 pm
Forum: Mathematica
Topic: [Question] Perimeter
Replies: 11
Views: 245

Re: [Question] Perimeter

B.Goode wrote:
Tue May 22, 2018 8:55 pm
(Still not sure why this is in a Raspberry Pi forum.)
I think the idea is to build a GPS surveying tool using Raspberry Pi. Green's theorem is surely the way to compute the area. Please read the whole Wikipedia article I linked to in my previous post.
by ejolson
Tue May 22, 2018 7:49 pm
Forum: Mathematica
Topic: [Question] Perimeter
Replies: 11
Views: 245

Re: [Question] Perimeter

Go to the Mathematics Department of your University and ask them to teach you some (Cartesian) coordinate geometry. Surely anyone in a University faculty doing this project would have already been taught coordinate geometry at school. Maybe even Calculus, but apparently not on this forum. Does Gree...
by ejolson
Tue May 22, 2018 6:48 pm
Forum: General programming discussion
Topic: Making readable modifyable code.
Replies: 284
Views: 32420

Re: Making readable modifyable code.

:) :) :) It is also more correct because returning 3.2 allows it to pass the unit test. try.c: In function ‘average’: try.c:13:10: warning: conversion from ‘double’ to ‘float’ changes value from ‘3.2000000000000002e+0’ to ‘3.20000005e+0f’ [-Wfloat-conversion] return 3.2; ^~~ It should be 3.2F 3.2 i...
by ejolson
Tue May 22, 2018 5:56 pm
Forum: General programming discussion
Topic: Making readable modifyable code.
Replies: 284
Views: 32420

Re: Making readable modifyable code.

Nope. thinkpad:Desktop simon$ cat > foo.c <<EOF > // Not guaranteed 100% correct, but very simple and efficient. > float average(float * values, int count) { > return 4; > } > EOF thinkpad:Desktop simon$ clang -c -std=c99 -Wall -Wunused-argument -Werror -o foo.o foo.c thinkpad:Desktop simon$ Try tu...
by ejolson
Tue May 22, 2018 4:30 pm
Forum: General programming discussion
Topic: Making readable modifyable code.
Replies: 284
Views: 32420

Re: Making readable modifyable code.

// Not guaranteed 100% correct, but very simple and efficient. float average(float * values, int count) { return 4; } In modern C that should be written float average(int count,float values[count]) { return 3.2; } which is simpler because it avoids the explicit use of pointers. It is also more corr...
by ejolson
Tue May 22, 2018 3:46 pm
Forum: Other languages
Topic: .NET Core - Raspbian or Win10IoT?
Replies: 78
Views: 3295

Re: .NET Core - Raspbian or Win10IoT?

jahboater, When comparing JS against C perhaps you should use a similar recent version of the C compiler (gcc 8) to be fair? Who is to say I can't have volatile there? As I said at least twice now the fact that I have used a PRNG in there is beside the point. It's just an example of some code. Besi...
by ejolson
Tue May 22, 2018 8:12 am
Forum: General discussion
Topic: Pi Zero vs Cray-2 --- Bambi vs Godzilla who will win?
Replies: 7
Views: 437

Re: Pi Zero vs Cray-2 --- Bambi vs Godzilla who will win?

Plus the Cray-2's floating point performance may not have been quite as high as hyped - here's a link to a report on the real world performance of the Cray-2 at the NASA Ames Research Center. As you can see, they were lucky to hit 100 Mflops on most workloads. Note that a naive implementation of Li...
by ejolson
Tue May 22, 2018 5:27 am
Forum: Troubleshooting
Topic: NFS boot authentication failure
Replies: 5
Views: 133

Re: NFS boot authentication failure

For info, backups were made with rsync -aAXvr ..... - which should fully preserve all permissions and ownership, and the NFS drive is ext4 formatted. If you are using rsync to backup the root filesystem of one computer using a different computer, you may want to specify the --numeric-ids option so ...
by ejolson
Tue May 22, 2018 5:05 am
Forum: General discussion
Topic: Pi Zero vs Cray-2 --- Bambi vs Godzilla who will win?
Replies: 7
Views: 437

Re: Pi Zero vs Cray-2 --- Bambi vs Godzilla who will win?

by comparing a mid nineteen-eighties Crey-2 supercomputer with a Raspberry Pi Zero. Thanks for the great idea. This may be more a demonstration of the importance of mathematics and algorithms: the Chudnovsky algorithm for calculating Pi did not exist until 1989. Coolnesss factor aside, the Cray 2 h...
by ejolson
Mon May 21, 2018 11:54 pm
Forum: Other languages
Topic: .NET Core - Raspbian or Win10IoT?
Replies: 78
Views: 3295

Re: .NET Core - Raspbian or Win10IoT?

No. Were your timings performed with a Raspberry Pi and if so what kind? Changing the inner loop to read for (int hw=0;hw<SIZE*SIZE;hw++){ if(hw==SIZE*SIZE/3) a[hw] = ((a[hw] * 42) + next()) % 100000; else next(); } avoids most of the memory accesses while preserving the computation of the one valu...
by ejolson
Mon May 21, 2018 10:57 pm
Forum: General discussion
Topic: 3B+ as a Wireless Access Point
Replies: 17
Views: 925

Re: 3B+ as a Wireless Access Point

At that time I plan to reduce the clock speed to 1200 Mhz and the memory speed to 450 Mhz. Maybe that's not necessary. Does anyone have other ideas how to improve stability? Reducing clock speed didn't seem to help. I've now switched the upstream and downstream WiFi devices. The built-in WiFi is no...
by ejolson
Mon May 21, 2018 8:49 pm
Forum: Other languages
Topic: .NET Core - Raspbian or Win10IoT?
Replies: 78
Views: 3295

Re: .NET Core - Raspbian or Win10IoT?

Row-major vs column-major array access? Since only the SIZE*SIZE/3 element is printed, you don't need an array at all. Just kick the random number generator SIZE*SIZE-1 times between each iteration and update only the relevant number you need for the answer. If you don't care about the exact sequen...
by ejolson
Sun May 20, 2018 11:10 pm
Forum: General discussion
Topic: What is the UUID scheme?
Replies: 12
Views: 484

Re: What is the UUID scheme?

As well as each filesystem having a UUID, each partition also has its own, separate UUID. Therefor blkid and lsblk show the partition UUID and filesystem UUID in certain places. I think the UUID system may break down when creating backup images using diskimager or dd to copy entire SD cards--sudden...
by ejolson
Sat May 19, 2018 11:03 pm
Forum: General discussion
Topic: Just throwing this out there: backdir
Replies: 23
Views: 1147

Re: Just throwing this out there: backdir

I'm not interested in any of the version control stuff or in collaboration. It is a good point that small-scale single-developer projects are not the kind of projects that BitKeeper or git were designed for. At the same time, due to a lack of annoying advertising, Github turns out to be a reasonabl...
by ejolson
Sat May 19, 2018 7:58 pm
Forum: General discussion
Topic: Just throwing this out there: backdir
Replies: 23
Views: 1147

Re: Just throwing this out there: backdir

Heater wrote:
Sat May 19, 2018 6:35 pm
What, you did not change to using git then?

:)
Maybe try BitKeeper as it is now open source. Which you prefer is a competition between not-invented-here, worse-is-better and the-right-thing approaches to software design.
by ejolson
Sat May 19, 2018 5:51 pm
Forum: Advanced users
Topic: How to convert Images from database(cloud) to timelapse video via raspberry pi?
Replies: 2
Views: 98

Re: How to convert Images from database(cloud) to timelapse video via raspberry pi?

hye, my project is about timelapse but we are not using the rpi camera to capture the images instead we are using DSLR camera for some reasons. once it captures, the images would be saved into the database. How could we actually use the images from the database to convert into a video by giving the...
by ejolson
Sat May 19, 2018 5:28 pm
Forum: General programming discussion
Topic: Python VS Java
Replies: 4
Views: 2380

Re: Python VS Java

What attracts me to Python for my analysis work is the "full-stack" of tools that are available by virtue of being designed as a general purpose language vs. R as a domain specific language. Welcome to the forum! You've presented a nicely thought out argument for Python. Even though the person who ...
by ejolson
Fri May 18, 2018 4:03 am
Forum: General programming discussion
Topic: How do I protect my code?
Replies: 32
Views: 1922

Re: How do I protect my code?

There is a similar recent discussion here: https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=203506 It includes a reference to a possible hardware encryption device. The per-unit cost of that device might help you evaluate the economics of your development. [This information is provided purel...
by ejolson
Thu May 17, 2018 9:43 pm
Forum: Troubleshooting
Topic: rasberri pi 3 and Zero W keeps crashing
Replies: 19
Views: 475

Re: rasberri pi 3 and Zero W keeps crashing

Any luck with reproduce? Am I just really unlucky with my first raspberries or is this kind of instability problems kind of common here? Really surprised that 2 out of 2 are failing to have a longer uptime than a day As these Pi computers are older than the newest 3B+, they should both be able to b...
by ejolson
Thu May 17, 2018 8:55 pm
Forum: Troubleshooting
Topic: broken filesystem, e2fsck can not fix things
Replies: 31
Views: 2783

Re: broken filesystem, e2fsck can not fix things

Hmmm raspi-config => "this pi can not be overclocked". Probably a limitation of Kedei image (probably to avoid SPI issues) I think that's a limitation of the raspi-config menu system. What worked for me was to add the line arm_freq=900 to the /boot/config.txt file and reboot. This makes the Pi 3B c...

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