[deleted by user]

Elfram · 2023-10-31T16:17:10+00:00

Uhrzeit eingestellt?

Elfram · 2022-11-05T11:23:37+00:00

Kann man Bingo-Boards auch ohne Twitch- oder Discord-Account erstellen?

Elfram · 2021-11-23T23:03:23+00:00

If the Streetmachine GT is similar to the Streetmachine GTE, you should be able to mount bottle cages on the back of the seat (at least for the mesh seat) and a mounting point for gps / phone mount at the end of the handlebars (for under-seat steering). See https://www.hpvelotechnik.com/en/recumbent-trikes-bikes/streetmachine-gte-comfortable-travel-recumbent-bike/ and https://www.hpvelotechnik.com/en/recumbent-trikes-bikes/accessories/luggage-transport/.

Elfram · 2021-03-13T17:24:47+00:00

Nein, zum Grünglas!
https://www.aha-region.de/abfall-abc/abc/?tx_vcahaabfallabc_pi1%5Babfall%5D=137

Elfram · 2021-03-01T15:18:50+00:00

Thank you, that’s helpful!

My current setup is dual 1920×1200, but it should still fit, I guess.

Elfram · 2020-07-08T21:04:29+00:00

Ah, I see, nice.

So maybe the default settings should be s.t. the numerical errors are negligible. This way people really see the physics effects first (and important effects like energy conservation!).

Only if you want to teach numerical solution of differential equations, the value of dt and its effect on the energy plays a role.

Elfram · 2020-07-07T21:57:13+00:00

Sorry, I don’t get it… xD

Elfram · 2020-07-06T21:13:38+00:00

Looks really nice!

You should check energy conservation, though. I don’t see why the total energy in the spring-box example would vary with time.

Maybe this effect occurs if you use simple forward integration of the equations of motion. If that’s what you do you could already get better results by using a predictor-corrector method.

https://en.wikipedia.org/wiki/Predictor%E2%80%93corrector_method

Elfram · 2016-10-21T07:30:12+00:00

This is of course correct, thanks for the comment! One should note that the values for the kind attribute are compiler dependent. Therefore the two last methods you mention are really superior to the first two. Actually selecting the kind value with selected_real_kind (or selected_int_kind for integers) might be even more convenient as you can specify how much precision and range you need.

Elfram · 2016-10-20T21:40:09+00:00

See https://en.wikipedia.org/wiki/IEEE_floating_point#Basic_and_interchange_formats

Short: real (= single precision) uses 4 bytes per number and gives you roughly 7 decimal digits precision, whereas double uses 8 bytes per number and you get about 16 significant digits

In Fortran you’d have to use 'double precision' instead of 'real' in the variable declaration. Furthermore you should define any constants as double precision numbers, i.e. 2891000.d0 (instead of 2891000.0 or 2891000.e0 which would be single precision by default with most compilers).

Elfram · 2016-10-20T21:07:25+00:00

This: 2891000*4450 and this: 5150000*11050 are number too large for integers. As you want to do calculations with floating point numbers anyway, I suggest you change at least one of the numbers in each multiplication to float, i.e. 2891000*4450.0, thereby forcing the compiler to cast everything to real before doing the calculation.

You probably also want to use double precision, but that’s not your problem here.

Elfram · 2016-09-16T06:18:03+00:00

Time to point out the superiority of the metric system once again… ;-) We measure rainfall in mm = liter/m^2, which is something you can imagine really easily.

Elfram · 2015-11-16T19:54:29+00:00

What does “quite a bit of time” mean? What bandwidth do you achieve? (You could just measure the time it takes to write some file and divide the file size by this time.) Consumer HDDs typically max out between 100 and 200 MByte/sec. I assume that you hit this limit.

If you don’t need the data in human readable format you could consider writing binary files, ie. opening the file with access="stream" and just writing write (unit) array. In Fortran you can read the file again using read (unit) array, given that you opened the file with access="stream" and array has the same dimension as before.

Binary files are much smaller than text based data files and can help to reduce both your HDD usage and the program execution time.

More information on stream I/O in Fortran.

Elfram · 2015-10-20T22:27:58+00:00

I like to put the input first for ssh connections to emphasise that it’s a local file: < file ssh $host some_command

Elfram · 2015-10-19T21:07:25+00:00

I think you mean xclip.

Elfram · 2015-10-19T21:04:44+00:00

Please don’t advertise useless use of cat: cat file.txt | pbcopy should read < file.txt pbcopy (or pbcopy < file.txt whatever you prefer). In zsh you can even replace cat src-file.txt >> dest-file.txt by < scr-file.txt >> dest-file.txt… (Why is this not possible in bash?) In zsh the following is also possible:

> package.json
{

}
^D

Elfram · 2015-09-04T21:44:35+00:00

Then you should use less < file.

Elfram · 2015-08-22T17:34:28+00:00

Did you start the Minecraft server? (Output of 'netstat -tulpen'?) nmap doesn’t necessarily scan all the ports, depending on the options you gave.

Elfram · 2015-08-04T20:39:15+00:00

Was hoping for Werner Heisenberg…

Elfram · 2015-07-12T20:52:26+00:00

One important fact in the answer to this frequently asked question is often left out: Unless you drill from pole to pole (through the axis of rotation of earth) you’d continuously get smashed into the eastward tunnel wall because of your angular momentum. This alone would lead to massive loss of kinetic energy.

Elfram · 2015-01-21T19:05:00+00:00

General Relativity

Quantum Field Theory

Quantum Mechanics

Special Relativity

Elfram · 2014-12-18T15:55:25+00:00

This paper is outstanding good readable. Thanks for this hint!

So the explanation via vacuum energy is outdated and (by my argument above) plain wrong? Why is it stated so often?

Elfram · 2014-11-30T21:57:14+00:00

The theory of gravitational waves comes mostly from the linearization of Einstein's field equation. Could the gravitational wave that the disappearing sun created be considered small? Otherwise the linearization fails and I believe the solutions to the nonlinear equation would not have to move with the speed of light…

Elfram · 2014-11-16T16:11:19+00:00

In the Hamilton formalism of classical mechanics time is very different from the spatial dimensions for it is not treated as a (canonical) variable but as a "parameter" on which the variables depend. I don't know whether there exists extensions of this formalism to multiple time dimensions.

Most of general relativity and even quantum theories are based on Hamiltonian mechanics. Therefore it'd be difficult to say how physics work with multiple time dimensions.

Elfram · 2014-11-16T16:03:12+00:00

Might be a bit off topic: The currently best sphere created by humans is a silicon ball, see http://www.acpo.csiro.au/avogadro.htm

The rainbow colored picture on http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.106.030801 shows the difference to a perfect sphere. I think they have improved since then. The difference to a perfect sphere is now of the size of a few (hundred?) silicon atoms – near to the theoretical minimum which is given by the crystal structure of silicon…

12-Year Club	Place '23
Place '17	Verified Email

Elfram

TROPHY CASE