Saturday, February 23, 2013

Which Correlation to use?

Summarized in the screen shot below: Which correlation to use when you have different types of data. This in no sense is complete, because you first need to understand the behaviour (or at least have a sense of it) of data before applying the statistical tools such as this.


Wednesday, February 13, 2013

Syntax vs Semantics


Semantics ~ Meaning
Syntax ~ Symbolic representation
So two programs written in different languages could do the same thing (semantics) but the symbols used to write the program would be different (syntax).
A compiler will check your syntax for you (compile-time errors), and derive the semantics from the language rules (mapping the syntax to machine instructions say), but won't find all the semantic errors (run-time errors, e.g. calculating the wrong result because the code says add 1 instead of add 2).

Actually there are not two levels but three:
  • lexical level: how characters are combined to produce language elements ( i and f produces if)
  • syntactical level: how language elements are combined to produce language expressions ( if(42,==answer and ) produces a conditional statement)
  • semantic level: how language expressions are converted to CPU instructions in order to form a meaning (a conditional statement allows to execute one branch or the other depending on the result of the boolean expression)

Syntax refers to formal rules governing the construction of valid statements in a language. 
Semantics refers to the set of rules which give the meaning of a statement.

Sources: http://programmers.stackexchange.com/questions/113800/whats-the-difference-between-syntax-and-semantics


What Does Parsing Mean?

This may not be complete explanation but i find it helpful to understand:


Parsing is the process of analyzing text made of a sequence of tokens to determine its grammatical structure with respect to a given (more or less) formal grammar.
The parser then builds a data structure based on the tokens. This data structure can then be used by a compiler, interpreter or translator to create an executable program or library.
alt text
If I gave you an english sentence, and asked you to break down the sentence into its parts of speech (nouns, verbs, etc.), you would be parsing the sentence.
That's the simplest explanation of parsing I can think of.
That said, parsing is a non-trivial computational problem. You have to start with simple examples, and work your way up to the more complex.

Source: http://stackoverflow.com/questions/2933192/whats-the-best-way-to-explain-parsing-to-a-new-programmer

Saturday, January 19, 2013

Configuring Pidgin for Gtalk on Ubuntu

Default settings may not work for you like they did not for me. Here is what worked for me:
Once you have setup your account change the following settings on
accounts->abc@gmail.com->edit account
Basic->Protocol set to XMPP
Advanced->Connect port to 443
Advanced->Talk Port to talk.google.com
Advanced->Connection Security to old-style SSL

You might also want to go to
Tools->Plugins->Libnotify Popups ->Configure Plugin-> Uncheck Buddy signs on, to disable annoying notifications every time somebuddy comes online.

Friday, January 18, 2013

Solved: Ubuntu Touchpad Problem on Vaio VGN-CS24GH

This is a little off from the topics of this blog but this bug troubled me so much that I had to put the solution that worked, out. Here is what I did:

Run the following commands on terminal:

sudo modprobe -r psmouse 
sudo modprobe psmouse proto=imps
sudo gedit /etc/modprobe.d/touchpad.conf

Write the following line in file touchpad.conf:
options psmouse proto=imps

Close the file. That's it!
As of now this is working perfectly on my laptop, Sony Vaio VGN-CS24GH, I hope it works for you too!

Compiling C, C++ Programs on Ubuntu

If you are a developer you need C and C++ Compiler for your development work.In ubuntu you can install the build-essential for C and C++ compilers.

Install C and C++ Compilers in Ubuntu

sudo aptitude install build-essential

This will install all the required packages for C and C++ compilers

Testing C and C++ Programs

Compiling Your first C Programs

Now you need to open first.c file

sudo gedit first.c

add the following lines save and exit the file




Firstly compile the code using the following command

cc -c first.c

that would produce an object file you may need to add to the library.

then create an executable using the following command

cc -o first first.c

Now run this executable using the following command

./first

Output should show as follows

Hello, world


Compiling your first C++ program

If you want to run c++ program follow this procedure

g++ is the compiler that you must use.

you should use a .cpp file extension rather than a .c one

You need to create a file

sudo gedit first.cpp

add the following lines save and exit the file




Run your C++ Program using the following command

g++ first.cpp -o test

./test

Output should show as follows

Hello World!


OR 


1. Install the 'build-essential' package.
$ sudo apt-get install build-essential

2. Write your first C program.
gedit myhello.c
paste this code into it, and save

#include <stdio.h>

main()
{
printf("Hello Ubuntu Lover!\n");
}


3. Compile your first C program

$ gcc myhello.c -o myhello


4. Run your first C program

$ ./myhello
Hello Ubuntu Lover!


5. Write your first C++ program
gedit myhello.cpp
paste this code into it, and save
#include <iostream>
using namespace std;

int main()
{
cout << "Hello Ubuntu Lover in C++" << endl;
return 0;
}

6. Compile your first C++ program
g++ myhello.cpp -o myhellocpp

7. Run your first C++ program
$ ./myhellocpp
Hello Ubuntu Lover in C++


Source of information:
 
  1. How to write and run c/c++ programs on ubuntu
  2. How to Install C and C++ Compilers in Ubuntu and testing your first C and C++ Program