repats blog

Nullstellenberechnung in Lua

Posted on 16. Dezember 2013 Comments

Nachdem ich 2011 schonmal ein paar Methoden zur numerischen Nullstellenberechnung in MATLAB online gestellt hatte, hier nur dieselben Beispiele in Lua. Ich habe mit Lua gerade erst angefangen und eigentlich erstmal zur Übung nur den Code übersetzt. Der Code ist natürlich auf GitHub. Eine gute Lua Referenz ist Learn Lua in 15 Minutes von @tylerneylon.

Wie im letzten Beispiel habe ich diese Funktion benutzt:

Ableitung zur Nullstellenberechnung Beipiel

Außer bei Newton(da braucht man noch die Ableitung) sieht das dann in Lua so aus.

function f(x)
  return x^6-x-1
end

Zusätzlich habe ich noch die Genauigkeit Eta global festgesetzt:

eta = 0.00001

Bisektion

function bisection(a,b)
  local i = 0

  if (f(b)*f(a)<0) then
    while (math.abs(b-a)>eta) do
      if (f((a+b)/2)*f(a)>0) then
        a = ((a+b)/2)
      else
        b = ((a+b)/2)
      end
      i = i + 1
    end
    return ((a+b)/2)
  end
end

Newtonverfahren

function newton(x)
  local i = 0
  local diff = 1
  while (diff>eta) do
    nullstelle = x
    t1, t2 = f(x)
    x = x - (t1/t2)
    i = i+1
    diff = math.abs(x-nullstelle)
  end
  return x
end

function f(x)
  return x^6-x-1, 6*x^5-1
end

Regula Falsi

function regula_falsi(a,b)
  local i = 0
  local diff = 1
  if (f(b)*f(a)<0) then
    nullstelle = a
     while (diff > eta) do
      x = (a*f(b)-b*f(a))/(f(b)-f(a));
      if (f(x)<0) then
        a = x
      else
        b = x
      end
      diff = math.abs(x-nullstelle)
      nullstelle = x
      i = i+1
    end
  end
  return nullstelle
end

Sekantenverfahren

function secant(a,b)
  local i = 0
  while(math.abs(b-a)>eta) do
    nullstelle = b
    b = b-f(b)*(b-a)/(f(b)-f(a))
    a = nullstelle
    i = i+1
  end
  return ((a+b)/2)
end

10 best Android apps for the paranoid

Posted on 15. Dezember 2013 Comments

So I compiled a few apps that even the most paranoid people would feel safe to use. Privacy is mostly enforced through encryption but beware: if you don’t use encryption correctly by e.g. chosing a weak password, it’s totally useless. You can download from Google Play (GP) or F-Droid (FD)

TextSecure (GP)

TextSecure encrypts your text messages(SMS) locally. Also, if your partner also has TextSecure, you can encrypt the messages, so not even the carrier could intercept them.

update: No SMS encryption functionality anymore, but this app is now called Signal and can still encrypt the SMS and message database on the phone. For SMS encryption use Silence (GP).

textsecure

Cost: free

RedPhone (GP)

RedPhone is basically an open source Skype replacement with even better encryption. It’s dead simple to use. If a contact in your phonebook also uses RedPhone, you will be asked if you want to upgrade to a secure call.

update: Now merged with TextSecure in the Signal Messenger App.

redphone

Cost: free

Google Authenticator (GP)

Whether it’s your bank, your WordPress blog, github, Dropbox or facebook. Two factor authentication with One Time Passwords(OTPs) is getting popular! With this app, you will not only need your password to login, but a code from your smartphone that’s generated and valid for 30 seconds. Just in case your phone gets stolen or lost, make sure to print out extra backup code. Don’t want them laying around your house? Use the next app!

Cost: free

EDSLite (GP)

EDSLite works much like Truecrypt/Veracrypt for your computer. You can create containers, where you can store your Pins, Tans, Backup OTP Backup Codes and more. Because TrueCrypt can read those containers you can just save them to your Dropbox and keep them in sync with your computer. If you don’t trust Dropbox, maybe the next app is for you.

update: Use Veracrypt instead of Truecrypt, since Truecrypt is not actively developed anymore. EDS can use both.

Cost: free

ownCloud (GP/FD)

ownCloud is an app that works with your owncloud installation. You can download your private cloud and host it from home on a Rapberry Pi or chose a hosted solution in a data center that you trust.

Cost: 0.79€

F-Droid

So, from where should you download all these apps? Trust Google or Amazon that the binaries you’re getting are what the developers uploaded? f-droid.org is another alternative app store that you might consider to trust. The apps are all open source and you can probably even get a couple of apps for free that would cost a few cents in the Google Play Store.

Cost: free

Threema (GP/Website)

Threema is probably the best app available for secure encrypted messaging; it works very much like Whatsapp. The servers are in Switzerland. The only downturn is: it’s not open source. But: you can verify that the encryption works correctly. If you just add a contact with his/her Threema ID, the contact appears read. If you sync your phonebook with Threema(your phone number is only transmitted as a hash) and Threema recognizes a contact, it’s getting orange. And if you meet your contact in person and scan his QR-code, the contact finally turns green. This is the most paranoid messaging app I’ve seen.

Cost: 1.60€

k-9 Mail (GP/FD)

If you want to send only encrypted emails, this is for you. Together with the APG app, it’s super easy to send encrypted and receive/decrypt emails.

Cost: free

Built-in Android encryption

With Android 4.x on you can encrypt your whole device. Make sure you chose and remember a good password or PIN.

Cost: free

NoteCipher (GP/FD)

Evernote is great for keeping your notes in sync. But if you want to keep them secret, you might want to consider using this app. Every entry is encrypted via sqlcipher with AES 256.

Cost: free

More stuff

Heml.is looks promising but has been under development for quite some time now. Hope to hear more soon.
- Heml.is is dead.
Telegram is another open source messaging app. The encryption only works, when both participants are online, so be careful.
- It might or might not be sure, check out this blog post and this blog post
Droid-Break has a lot more high quality open source apps

GP: Google Play, FD: F-Droid, Pictures from play.google.com

Show Pictures in a Form on a Table with Report in APEX

Posted on 10. Dezember 2013 Comments

The table is called WPDBD_TEIL. The primary key is TID. In WPDBD_TEIL there is a column called BILD(german: picture/image) from type BLOB.

First click on your form and keep the name of the picture in mind. In this case, it’s P9_BILD.

Then go to your report, click on edit for the whole report and use the following code

select "TID", 
"TNAME",
"PREIS",
decode(nvl(dbms_lob.getlength("BILD"),0),0,null, '<img height="100px" width="100px" src="'||apex_util.get_blob_file_src('P9_BILD',TID)||'" />') "BILD"
from "#OWNER#"."WPDBD_TEIL"

If you’d open the report now, you only get the HTML Code. So you have to change the way APEX displays the entry. So go to the report, click on BILD and change Display as Text to Report Standard Column

The form I used was the following.

Also, in the last page of creating the form, you have to chose your own primary key, not the ROWID.

How to compile async for scala with sbt

Posted on 6. Dezember 2013 Comments

SBT is the build tool for Scala, much like Maven or Ant is for Java. Scalas async library uses it for compiling. You could just it from the source or compile it into a handy .jar file. That’s where SBT comes in. The Scala version I used it 2.10.3, SBT in version 0.13.0 and async in 0.9.0. The build.sh in the repository didn’t work for me.

Clone the lastest version of the GitHub repository: https://github.com/scala/async

git clone https://github.com/scala/async.git

Then download and install sbt from scala-sbt.org. For Ubuntu 12.04 I just used the .deb package.

wget http://repo.scala-sbt.org/scalasbt/sbt-native-packages/org/scala-sbt/sbt/0.13.0/sbt.deb

And install it.

sudo dpkg -i sbt.deb

Then open it in the same folder you cloned the git repository:

repat@laptop:~/asynctest/async$ sbt
Loading /usr/share/sbt/bin/sbt-launch-lib.bash
[info] Loading project definition from /home/repat/asynctest/async/project
[info] Updating {file:/home/repat/asynctest/async/project/}async-build...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Set current project to scala-async (in build file:/home/repat/asynctest/async/)
>

Maybe a couple of updates will appear here and depending on your internet connection it might actually take a while.
Once you get the > sign type compile and this will happen:

[info] Updating {file:/home/repat/asynctest/async/}async...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Compiling 15 Scala sources to /home/repat/asynctest/async/target/scala-2.10/classes...
[warn] there were 2 feature warning(s); re-run with -feature for details
[warn] one warning found
[success] Total time: 28 s, completed 06.12.2013 19:22:09

You will now have the compiled .class files in …/async/target/scala-2.10. The get the .jar do the following.

> publish
[info] Packaging /home/repat/asynctest/async/target/scala-2.10/scala-async_2.10-0.9.0-SNAPSHOT-sources.jar ...
[info] Done packaging.
[info] Wrote /home/repat/asynctest/async/target/scala-2.10/scala-async_2.10-0.9.0-SNAPSHOT.pom
[info] :: delivering :: org.scala-lang.modules#scala-async_2.10;0.9.0-SNAPSHOT :: 0.9.0-SNAPSHOT :: integration :: Fri Dec 06 19:25:16 CET 2013
[info] 	delivering ivy file to /home/repat/asynctest/async/target/scala-2.10/ivy-0.9.0-SNAPSHOT.xml
[info] Main Scala API documentation to /home/repat/asynctest/async/target/scala-2.10/api...
[warn] there were 2 feature warning(s); re-run with -feature for details
model contains 29 documentable templates
[warn] /home/repat/asynctest/async/src/main/scala/scala/async/Async.scala:11: Could not find any member to link for "scala.concurrent.Future".
[warn] /**
[warn] ^
[warn] /home/repat/asynctest/async/src/main/scala/scala/async/internal/FutureSystem.scala:9: Could not find any member to link for "scala.async.AsyncBase".
[warn] /**
[warn] ^
[warn] three warnings found
[info] Main Scala API documentation successful.
[info] Packaging /home/repat/asynctest/async/target/scala-2.10/scala-async_2.10-0.9.0-SNAPSHOT-javadoc.jar ...
[info] Done packaging.
[trace] Stack trace suppressed: run last *:publish for the full output.
[error] (*:publish) java.io.IOException: Access to URL https://oss.sonatype.org/content/repositories/snapshots/org/scala-lang/modules/scala-async_2.10/0.9.0-SNAPSHOT/scala-async_2.10-0.9.0-SNAPSHOT.pom was refused by the server: Unauthorized
[error] Total time: 12 s, completed 06.12.2013 19:25:27

I’m not sure why it stops with an error here or rather, why access is denied to that repository. Anyway, the scala-async_2.10-0.9.0-SNAPSHOT.jar file is now in …/async/target/scala-2.10.

As mentioned in the error message, you get the stacktrace with last *:publish. I leave this here so people can find it via google.

last *:publish 
java.io.IOException: Access to URL https://oss.sonatype.org/content/repositories/snapshots/org/scala-lang/modules/scala-async_2.10/0.9.0-SNAPSHOT/scala-async_2.10-0.9.0-SNAPSHOT.pom was refused by the server: Unauthorized
	at org.apache.ivy.util.url.AbstractURLHandler.validatePutStatusCode(AbstractURLHandler.java:79)
	at org.apache.ivy.util.url.BasicURLHandler.upload(BasicURLHandler.java:231)
	at org.apache.ivy.util.FileUtil.copy(FileUtil.java:150)
	at org.apache.ivy.plugins.repository.url.URLRepository.put(URLRepository.java:84)
	at org.apache.ivy.plugins.repository.AbstractRepository.put(AbstractRepository.java:130)
	at org.apache.ivy.plugins.resolver.RepositoryResolver.put(RepositoryResolver.java:234)
	at org.apache.ivy.plugins.resolver.RepositoryResolver.publish(RepositoryResolver.java:216)
	at sbt.IvyActions$$anonfun$publish$3.apply(IvyActions.scala:258)
	at sbt.IvyActions$$anonfun$publish$3.apply(IvyActions.scala:257)
	at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:772)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
	at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:771)
	at sbt.IvyActions$.publish(IvyActions.scala:257)
	at sbt.IvyActions$$anonfun$publish$1$$anonfun$apply$1.apply$mcV$sp(IvyActions.scala:93)
	at sbt.IvyActions$$anonfun$publish$1$$anonfun$apply$1.apply(IvyActions.scala:93)
	at sbt.IvyActions$$anonfun$publish$1$$anonfun$apply$1.apply(IvyActions.scala:93)
	at sbt.IvyActions$.withChecksums(IvyActions.scala:102)
	at sbt.IvyActions$.sbt$IvyActions$$withChecksums(IvyActions.scala:97)
	at sbt.IvyActions$$anonfun$publish$1.apply(IvyActions.scala:93)
	at sbt.IvyActions$$anonfun$publish$1.apply(IvyActions.scala:87)
	at sbt.IvySbt$Module$$anonfun$withModule$1.apply(Ivy.scala:116)
	at sbt.IvySbt$Module$$anonfun$withModule$1.apply(Ivy.scala:116)
	at sbt.IvySbt$$anonfun$withIvy$1.apply(Ivy.scala:104)
	at sbt.IvySbt.sbt$IvySbt$$action$1(Ivy.scala:51)
	at sbt.IvySbt$$anon$3.call(Ivy.scala:60)
	at xsbt.boot.Locks$GlobalLock.withChannel$1(Locks.scala:98)
	at xsbt.boot.Locks$GlobalLock.xsbt$boot$Locks$GlobalLock$$withChannelRetries$1(Locks.scala:81)
	at xsbt.boot.Locks$GlobalLock$$anonfun$withFileLock$1.apply(Locks.scala:102)
	at xsbt.boot.Using$.withResource(Using.scala:11)
	at xsbt.boot.Using$.apply(Using.scala:10)
	at xsbt.boot.Locks$GlobalLock.ignoringDeadlockAvoided(Locks.scala:62)
	at xsbt.boot.Locks$GlobalLock.withLock(Locks.scala:52)
	at xsbt.boot.Locks$.apply0(Locks.scala:31)
	at xsbt.boot.Locks$.apply(Locks.scala:28)
	at sbt.IvySbt.withDefaultLogger(Ivy.scala:60)
	at sbt.IvySbt.withIvy(Ivy.scala:101)
	at sbt.IvySbt.withIvy(Ivy.scala:97)
	at sbt.IvySbt$Module.withModule(Ivy.scala:116)
	at sbt.IvyActions$.publish(IvyActions.scala:87)
	at sbt.Classpaths$$anonfun$publishTask$1.apply(Defaults.scala:1094)
	at sbt.Classpaths$$anonfun$publishTask$1.apply(Defaults.scala:1093)
	at scala.Function3$$anonfun$tupled$1.apply(Function3.scala:35)
	at scala.Function3$$anonfun$tupled$1.apply(Function3.scala:34)
	at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
	at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:42)
	at sbt.std.Transform$$anon$4.work(System.scala:64)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18)
	at sbt.Execute.work(Execute.scala:244)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
	at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:160)
	at sbt.CompletionService$$anon$2.call(CompletionService.scala:30)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:724)
[error] (*:publish) java.io.IOException: Access to URL https://oss.sonatype.org/content/repositories/snapshots/org/scala-lang/modules/scala-async_2.10/0.9.0-SNAPSHOT/scala-async_2.10-0.9.0-SNAPSHOT.pom was refused by the server: Unauthorized

Updating Owncloud News App with cron and Uberspace

Posted on 27. November 2013 Comments

Since it’s not possible to create a cronjob with the user the webserver is running under(as advised), I just created a cronjob with my user(crontab -e) and it works just fine.

[repat@uberspace]$ crontab -l
*/15 * * * * /package/host/localhost/php/bin/php -f /home/repat/html/owncloud/cron.php

The problem was the following: owncloud wouldn’t update my news and I didn’t think it was a cron problem, since I couldn’t update it manually(AJAX). Adding new feeds however did work. I still don’t get why manual updating doesn’t work , even with the Android app. Opening cron.php in the webbrowser didn’t work, although it did display {„status“:“success“}..turns out: it has to be called via CLI.

Unfortunately, I get an email every 15 minutes now… To disable that I added this above the cron entry:

MAILTO=""

Thanks to Raydiation and j-ed for helping me.

„Incomplete statements not supported yet, sorry, you’ll have to retype“ Error with Scala and Eclipse

Posted on 15. November 2013 Comments

I got this error defining the function

object test {
  val f:AnyVal => String = {
      case 10.0 => "10.0"
      case _: Double => "Double"
      case _: Int => "Int"
      case _: Byte => "Byte"
      case _ => "anything else"
}

-> Incomplete statements not supported yet, sorry, you’ll have to retype.

However, in REPL it worked just fine.

repat@laptop:~$ scala
Welcome to Scala version 2.10.3 (OpenJDK 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala>   val f:AnyVal => String = {
     |       case 10.0 => "10.0"
     |       case _: Double => "Double"
     |       case _: Int => "Int"
     |       case _: Byte => "Byte"
     |       case _ => "anything else"
     |   }
f: AnyVal => String = 

scala>

So aparrently the error is in Eclipse. I use the version 3.7.2. Have you tried turning it off and on again? 😉

How not to get the fork-me-on-github ribbon on facebook links

Posted on 7. November 2013 Comments

When you include one of these fork-me-on-github ribbons on your website and share the link on facebook, the little thumbnail that the link shows will most little be that ribbon. That’s because Facebook uses the Open Graph Protocol – also a facebook invention – to get this information. If there is non specified, it will use the first picture availble, which is most likely the github ribbon.

The solution is to use an image with at least 200x200px and the og:description tags for a text next to the picture. By the way: your website is more likely to be found on the facebook graph search if you do this right.

You specifiy it like this (for example droid-break.info):

<meta property="og:image" content="https://droid-break.info/droidbreak-logo-big.png" />
<meta property="og:locale" content="en_US" />
<meta property="og:title" content="Droid-Break"/>
<meta property="og:type" content="website"/>
<meta property="og:url" content="https://droid-break.info"/>
<meta property="og:site_name" content="Droid-Break.info - A list of free alternatives to proprietary android apps"/>
<meta property="og:description" content="A list of free alternatives to proprietary android apps"/>

OpenCV Examples mit Ubuntu 12.04

Posted on 6. November 2013 Comments

Um mir OpenCV erstmal ein bisschen anzuschauen habe ich diese Anleitung befolgt und erstmal meine eingebaute Webcam(/dev/video0) benutzt.

sudo apt-get install build-essential libavformat-dev ffmpeg libcv2.3 libcvaux2.3 libhighgui2.3 python-opencv opencv-doc libcv-dev libcvaux-dev libhighgui-dev

Als Beispielprogramm habe ich mir facedetection ausgesucht. Mithilfe dieser Anleitung habe ich den Befehl gefunden, um die Ausgabe zu testen:

cp -r /usr/share/doc/opencv-doc/examples .
cd examples/c
gunzip facedetect.cpp.gz
sh build_all.sh

Zum Starten benötigt man dann noch die XML Datei /usr/share/opencv/haarcascades/haarcascade_frontalface_alt.xml. Der Befehl lautet also:

$ ./facedetect --cascade="/usr/share/opencv/haarcascades/haarcascade_frontalface_alt.xml"

Damit öffnet er das Device /dev/video0. Man kann auch als weiteres Argument ein Bild mit angeben:

$ ./facedetect --cascade="/usr/share/opencv/haarcascades/haarcascade_frontalface_alt.xml" lena.jpg

MySQL Verbindungen in C++ mit mysqlpp

Posted on 6. November 2013 Comments

MySQL Server und Header installieren:

sudo apt-get install mysql-server  libmysqlclient-dev libmysql++-dev

In Eclipse C++-Projekt anlegen, Rechtsklick auf das Projekt:

Properties>C/C++-Build>Settings>Tool Settings>GCC C++ Compiler>Includes
Dort die Pfade /usr/include/mysql und /usr/include/mysql++ als Include paths eintragen.

Weiter unten unter GCC C++ Linker>Libraries>Libraries „mysqlpp“ eintragen und unter Library search paths ebenfalls /usr/include/mysql und /usr/include/mysql++.

Unter Miscellaneous dann noch bei Other objects die Datei /usr/lib/x86_64-linux-gnu/libmysqlclient.so angeben:

Beispieldatei: mysqlpptest.cpp

Credits: C++ with a shot of MySQL on Ubuntu 10.10

ActiveMQ mit C++ und Eclipse

Posted on 6. November 2013 Comments

Vorraussetzungen

Betriebsystem: Ubuntu 12.04
Eclipse Version: 3.7.2 „Indigo“
ActiveMQ-CPP Download
Beispiele

Vorbereitung

sudo apt-get update && apt-get upgrade && apt-get install build-essential autoconf libaprutil1-dev libapr1-dev

cd ~/Development

wget http://mirror.softaculous.com/apache/activemq/activemq-cpp/source/activemq-cpp-library-3.4.5-src.tar.gz

tar -xvzf activemq-cpp-library-3.4.5-src.tar.gz

cd activemq-cpp-library-3.4.5-src

./configure

make

ActiveMQ-CPP

Dann mit sudo make install auf dem lokalen Rechner installieren. Damit befinden sich dann die .so-Dateien in /usr/local/lib.

In Eclipse

Neu -> C++ Project
Rechtsklick Projekt -> Properties
C/C++ -> Build -> Settings -> GCC C++ Compiler -> Includes
Unter include paths Pfad von ActiveMQ-CPP: /home/user/workspace/activemq-cpp-3.4.5/activemq-cpp/src/main hinzufügen oder anpassen
Dort auch Pfad von APR hinzufügen: /usr/include/apr-1.0
Die beiden auch beim Linker als library search path hinzufügen oder anpassen
Als shared Object beim Linker /usr/local/lib/libactivemq-cpp.so hinzufügen

Beispiele

Die Projekte unter activemq-cpp-3.4.5/activemy-cpp/src/examples lassen sich jetzt kompilieren, allerdings kommt beim starten folgende Fehlermeldung:

./activeMQProducer: error while loading shared libraries: libactivemq-cpp.so.14: 
cannot open shared object file: No such file or directory

Der Fehler lässt sich mit folgendem Befehl beheben(credit):

export LD_LIBRARY_PATH=/usr/local/lib:${LD_LIBRARY_PATH}

Diesen Artikel hatte ich bereits vor einem Jahr(Ende 2012) geschrieben. Vielleicht gibt es neue Versionen der benutzen Software.