Introduction to android

ANDROID BASICS  

All you need to know before starting android programming ...

ANDROID is an open source  operating system that is based on a modified version of linux.

About its architecture 

1) LINUX KERNEL  -- It contains device driver for display, camera, memory .....

2)  LIBRARIES  -- developed in C/C++

some of them are --

SURFACE MANAGER - for display management

SQLITE   -- for database support

SSL --or security

WEBKIT  -- for web browsing

OpenGL/ES -- graphic library

FREETYPE -- it is used as font render in android

SGL -- scalable graphic library

LIBC -- standard C library

SSL -- secure socket layer

3) ANDROID RUNTIME 

Core libraries    &   DALVIK VIRTUAL MACHINE (DVM)

*   Program for android are written in java and compiled to byte code for JVM, which is then translated to Dalvik bytecode and  stored in .dex (dalvik executable) and .odex (optimized dalvik executable)

Succesor of Dalvik is ART Android Runtime which uses the same byte code and  .dex file but not .odex.

* Each app is a different user for  android OS.
* Each app is assigned a unique linux user ID which is used by the system & unknown to the app.
* It is possible to arrange for  2 apps to share the same linux user ID, in which they aare able to access each others files
* App with same user ID can also arrange to run in same linux process & share the same VM.


To be continued .....

Matrix & ITS Types

MATRIX :

"Matrix is nothing but the rectangular representation of data in the form of rows and columns inside square brackets "

• A row matrix is a matrix that has only one row.
• A column matrix is a matrix that has only one column.

Example :


To convert linear equations into matrix :

Each equation in the system becomes a row. Each variable in the system becomes a column. The variables are dropped and the coefficients are placed into a matrix. If the right hand side is included, it's called an augmented matrix. If the right hand side isn't included, it's called a coefficient matrix.

The system of linear equations ...

 x +  y -  z = 1

3x - 2y +  z = 3

4x +  y - 2z = 9

becomes the augmented matrix ...

	x	y	z	rhs
	1	1	-1	1
	3	-2	1	3
	4	1	-2	9

Type of Matrix :

1. ZERO/NULL Matrix :

2. UPPER  & LOWER TRIANGULAR MATRIX :

3. Diagonal Matrix  :

4. IDENTITY MATRIX:

5. SYMMETRIC MATRIX : 

* If a matrix is equal to its transpose matrix then it is called symmetric matrix.

                                                                  A = A^T

6. SKEW SYMMETRIC 

* If a matrix is equal to the negative of its transpose then it is called SKEW SYMMETRIC 

 A = -A^T

Example of skew symmetric :

7. Idempotent Matrix :

* A square matrix A is called idempotent matrix if   

A² = A

8. Involutory Matrix 

 A² = I