Robert Thompson

I get by in programming via experimentation and google. However, there are times where I wish I knew how to program more ‘proper’. I’ve been wanting to learn how to make iphone apps for some time now so thanks to davey I’ve been watching a few tutorial videos on objective-c. Many start with the basics which can be quite tedious, but I suffer through them to make sure I don’t miss any crucial information. Today I learned exactly what break & continue mean in the context of a for loop. I had an idea previously but never bothered to look up the formal definition. So lets for instance look at this for loop:

for (int i = 1; i < 5000; i++){
    if (i == 101)
    break;
    printf("The index value is %i\n",i);
}

for (int i = 1; i < 5000; i++){
    if (i % 5. == 0)
    continue;
    printf("The index value is %i\n",i);
}

which says that if the remainder of i/5 is equal to 0, then consider this specific loop iteration finished and move on to the next one without executing any of the code below. The % sign here is known as the modulus operator.

In summary:

break;    //DROPS OUT OF THE FOR LOOP COMPLETELY
continue; //COMPLETES CURRENT ITERATION AND MOVES ON TO THE NEXT

Turns out I was running my BLOB tests incorrectly by not telling gadget that the box size was not a cube. The periodic box was supposed to be x,y,z=[2000,2000,6000] but was simply registering as [2000,2000,2000]. Initially I didn’t think this would pose a problem since it was a periodic box, but I forgot to take into account the shockwaves propagating back into the initial blob and causing some unwanted disturbances. Anyway, by switching on three parameters in the makefile:

-DLONG_X=1.
-DLONG_Y=1.
-DLONG_Z=3.

ffmpeg -r 12 -i splash_%04d.png -c:v libx264 -crf 1 -pix_fmt
yuv420p -r 30 output.mp4

In doing some Kelvin-Helmholtz comparisons I have been trying to cook up a script that can stitch two movies together with ffmpeg. In order to determine how many frames I need I must do a simple subtraction in bash, but how?! Easy apparently…you just:

#!/bin/bash
BEG=10
END=400
NUM=$((END-BEG))
echo $NUM

and it will return the value 390. So how about that ffmpeg script?!

#!/bin/bash

FPS=12

BEG=10
END=50

DIR1=.
DIR2=.

PREFIX1=splash\_%04d.png
PREFIX2=splash\_%04d.png

MOV1=1.mov
MOV2=2.mov
FINAL=SIDEBYSIDE.mov

NUM=$((END-BEG))

if [ $END -gt 0 ]
  then
  PARAM="-vframes $NUM"
  else
  PARAM=""
fi

ffmpeg -start\_number $BEG -r $FPS -i $DIR1/$PREFIX1 $PARAM -vcodec qtrle $MOV1
ffmpeg -start\_number $BEG -r $FPS -i $DIR2/$PREFIX2 $PARAM -vcodec qtrle $MOV2

## SIDE BY SIDE ##
ffmpeg -i $MOV2 -vf "movie=$MOV1 [in1]; [in]pad=iw\*2:ih:iw:0[in0]; [in0][in1] overlay=0:0 [out]" -vcodec qtrle $FINAL

I ran a systematic comparison between vanilla SPH and DISPH using our latest version of the code. I include all the fancy physics such as EZW winds (momentum+energy) at 150km/s & 75km/s, feedback with typeIa,AGB, etc etc.

Let’s start with the phase differences:

SFRD:

GSMF:

m-Z relation:

fgas:

sSFR:

HMR:

timings:

density fields:

Apparently .npz files have a limit of ~4GB, which can be a problem when dealing with large datasets ($$600^3$$), so how do I write binary files of this size?! Looks like I need to migrate to HDF5…lol; here’s an example for read/write similar to npz:

import h5py
a = np.random.rand(1000,1000)
f = h5py.File('/tmp/myfile.hdf5')
f['a'] = a # <-- Save
f.close()

now that will write the file, lets open it

import h5py
f = h5py.File('/tmp/myfile.hdf5')
b = f['a']
#b = b[()]
f.keys() #shows all values in the dataset
f.close()

but the odd thing is, you can’t directly access the data here by just ‘b’. Instead there is a ton of information attached like b.shape, b.dtype, etc etc, all found here. Instead, you simply have to use the command

b.value

and that will output the data of the file.

Setting up a true VPN (and not just an SSH tunnel) on ubuntu isn’t exactly challenging, but took a little bit of dinkering around. The nice thing is that it works wel and will make things a bit easier when it comes to changing settings while sitting outside of my network, while ‘pretending’ I am inside of my network! I simply followed the straight forward instructions here.

It’s pretty amazing to see this at 3am somewhere over north eastern Canada. The sun is always shining up here during the winter months; lets hear it for circumpolar stars!

I’m heading away for a while and will need continued access to my server. Usually that means via ssh, but occasionally I have to VNC into the machine. The problem is - if the server goes down for any reason, when it comes back up the VNC server does not start until I login. So is there a way to set automatic login and lock the screen at the same time? Yes! This is linux, of course there is! Simply create a new file

/home/USERNAME/.config/autostart/screen_lock.desktop

and add the contents

[Desktop Entry] Type=Application Name=Lock Screen Exec=gnome-screensaver-command -l

and that was that, works like a charm. Courtesy of AskUbuntu.