Jiansen Lu's Computing Blog: August 2010

Tuesday, August 31, 2010

Microsoft Windows with the X Windows System

Microsoft Windows users may also require an X Windows display server for running applications with a graphical user interface. We recommend Xming-mesa. This application is used along with PuTTY (see below section).
To use Xming, first start up Xming as follows:
Start -> Programs -> Xming -> Xlaunch
Accept the default settings.
Now, to access a server, connect to the server using PuTTY. Most of the default PuTTY settings are ok except you must check the box "Enable X11 forwarding" under the X11 configuration category. PuTTY will prompt you for your username and password. Start the desired X-Windows application in the resulting terminal window.

OS X with the X Windows System
For the X Windows system, use the X11 application which comes with OS X. It may need to be separately installed from the operating system or downloaded from the Apple website. It will be in the Utilities folder which is in the Applications folder. Open X11, then from the "Applications" menu, choose "Terminal". In the terminal window that presents, enter the following replacing hostname as required (remember the -X!):
ssh -X hostaddress

Microsoft Windows with ssh
Microsoft Windows does not come with an ssh client program. Therefore, we recommend that you download and install PuTTY (terminal program) and WinSCP (file transfer program).

SPSS job interview questions

1. What is data view and variable view?

• In Data View, columns represent variables, and rows represent cases (observations).

• In Variable View, each row is a variable, and each column is an attribute that is associated with that variable.

2. What statistics analysis is included in SPSS?

Descriptive statistics: Cross tabulation, Frequencies, Descriptives, Explore, Descriptive Ratio Statistics
Bivariate statistics: Means, t-test, ANOVA, Correlation (bivariate, partial, distances), Nonparametric tests
Prediction for numerical outcomes: Linear regression
Prediction for identifying groups: Factor analysis, cluster analysis (two-step, K-means, hierarchical), Discriminant

3. How to calculate the effect of educational intervention to drug prescription?
We can input the drug prescription status (yes or no) before and after educational intervention. We can calculate the odds ratio using logistic regression in SPSS.

4. How to calculate the effect of educational intervention to drug dose in prescription?

We used a matched pair for magnitude of drug dose before and after intervention and analyze it using student t-test in SPSS.

Hypothesis test -- statistics

1) Null hypothesis:
The null hypothesis (denote by H₀) is a statement about the value of
a population parameter (such as mean), and it must contain the condition of equality and must be written with the symbol =, ≤, or ≤.

2. Alternative hypothesis
The Alternative hypothesis (denoted by H₁) is the statement that must be true if the null hypothesis is false.

Conclusion
a) Fail to reject the null hypothesis
b) Reject the null hypothesis.

Significance level
The probability of rejecting the null hypothesis when it is called
the significance level α , and very common choices are
α = 0.05 and α = 0.01

Example:
A sample of data for body temperature (n=106, x̄=98.20°, s =0.62),
for a 0.05 significance level, test the claim that the mean body temperature of health adults is equal to 98.6°F.

Solution: We have:
H₀: μ=98.6 (original claim) H₁ : μ≠98.6
As n>30, the central limit theorem indicates that the distribution of sample means can be approximated by a normal distribution
z= (x̄ - μ)/ (σ/√n) = (98.20-98.6)/(0.62/√106) = -6.64
The test is two-sided because a sample mean significantly less than or greater than 98.6 is strong evidence against the null hypothesis that μ=98.6.
α/2 = 0.025, the left critical z value = -1.96, right z critical value = 1.96. For z between -1.96 and 1.96, we fail to reject H₀.
As z = -6.64, we reject the reject H₀i.e. we reject the hypothesis that the mean body temperature of health adults is equal to 98.6°F.

Central Limit Theorem--statistics

As the sample size increases, the sampling distribution of sample
means approaches a normal distribution

If all possible random samples of size n are selected from a population with mean μ and standard deviation σ, the mean of the sample means is denoted by μ_x̄, so
μ_x̄ = μ
the standard deviation of the sample means is:
σ _x̄ = σ⁄ n

Example: Given that the population of men has normally distributed weights, with a mean of 173 lb and a standard deviation of 30 lb, find the probability that
a. if 1 man is randomly selected, his weight is greater than 180 lb.
b. if 36 different men are randomly selected, their mean weight is greater that 180 lb.

Solution: a) z = (x - μ)/ σ = (180-173)/30 = 0.23
For normal distribution P(Z>0.23) = 0.4090
b) σ _x̄ = σ/n = 20/√ 36 = 5
z= (180-173)/5 = 1.40
P(Z>1.4) = 0.0808

Binomial Probability Formula--statistics

P(x)= p^x q ^n-x n!/[(n-x)!x!]
where x = number of trials
x = number of successes among n trials
p = probability of success in any one trial
q = 1 -p

Example: Find the probability of getting 3 left-handed students in a class of 15 students, given that 10% of us are left-handed.
Solution: here n = 15, x=3, p =0.1, q =0.9
p(3) = 0.129, the probability is 12.9%

math formula in html

Superscript and Subscript

With the Tags

You can use the tag to create superscript text and to create su-script text. Or you can use the codes below.
Code: xx+1
Result: x^x+1
Code: xi+1

Result: x_i+1

With the Codes

Code: x²

Result: x²
Code: x⁴

Result: x⁴
More detail see the link

Special Characters in HTML

left single quote		‘	‘
right single quote		’	’
single low-9 quote		&sbquo;	‚
left double quote		“	“
right double quote		”	”
double low-9 quote		&bdquo;	„
dagger		&dagger;	†
double dagger		&Dagger;	‡
per mill sign		&permil;	‰
single left-pointing angle quote		&lsaquo;	‹
single right-pointing angle quote		&rsaquo;	›
black spade suit		&spades;	♠
black club suit		&clubs;	♣
black heart suit		&hearts;	♥
black diamond suit		&diams;	♦
overline, = spacing overscore		&oline;	‾
leftward arrow		←	←
upward arrow		↑	↑
rightward arrow		→	→
downward arrow		↓	↓
trademark sign	™	™	™
unused	-
horizontal tab
line feed
unused
space
exclamation mark	!		!
double quotation mark	"	"	"
number sign	#		#
dollar sign	$		$
percent sign	%		%
ampersand	&	&	&
apostrophe	'		'
left parenthesis	(		(
right parenthesis	)		)
asterisk	*		*
plus sign	+		+
comma	,		,
hyphen	-		-
period	.		.
slash	/	&frasl;	/
digits 0-9	0- 9
colon	:		:
semicolon	;		;
less-than sign	<	<	<
equals sign	=		=
greater-than sign	>	>	>
question mark	?		?
at sign	@		@
uppercase letters A-Z	A- Z
left square bracket	[		[
backslash	\		\
right square bracket	]		]
caret	^		^
horizontal bar (underscore)	_		_
grave accent	`		`
lowercase letters a-z	a- z
left curly brace	{		{
vertical bar	\|		\|
right curly brace	}		}
tilde	~		~
unused	-
en dash		–	–
em dash		—	—
unused	-
nonbreaking space
inverted exclamation	¡	¡	¡
cent sign	¢	¢	¢
pound sterling	£	£	£
general currency sign	¤	¤	¤
yen sign	¥	¥	¥
broken vertical bar	¦	¦ or &brkbar;	¦
section sign	§	§	§
umlaut	¨	¨ or &die;	¨
copyright	©	©	©
feminine ordinal	ª	ª	ª
left angle quote	«	«	«
not sign	¬	¬	¬
soft hyphen
registered trademark	®	®	®
macron accent	¯	¯ or &hibar;	¯
degree sign	°	°	°
plus or minus	±	±	±
superscript two	²	²	²
superscript three	³	³	³
acute accent	´	´	´
micro sign	µ	µ	µ
paragraph sign	¶	¶	¶
middle dot	·	·	·
cedilla	¸	¸	¸
superscript one	¹	¹	¹
masculine ordinal	º	º	º
right angle quote	»	»	»
one-fourth	¼	¼	¼
one-half	½	½	½
three-fourths	¾	¾	¾
inverted question mark	¿	¿	¿
uppercase A, grave accent	À	À	À
uppercase A, acute accent	Á	Á	Á
uppercase A, circumflex accent	Â	Â	Â
uppercase A, tilde	Ã	Ã	Ã
uppercase A, umlaut	Ä	Ä	Ä
uppercase A, ring	Å	Å	Å
uppercase AE	Æ	Æ	Æ
uppercase C, cedilla	Ç	Ç	Ç
uppercase E, grave accent	È	È	È
uppercase E, acute accent	É	É	É
uppercase E, circumflex accent	Ê	Ê	Ê
uppercase E, umlaut	Ë	Ë	Ë
uppercase I, grave accent	Ì	Ì	Ì
uppercase I, acute accent	Í	Í	Í
uppercase I, circumflex accent	Î	Î	Î
uppercase I, umlaut	Ï	Ï	Ï
uppercase Eth, Icelandic	Ð	Ð	Ð
uppercase N, tilde	Ñ	Ñ	Ñ
uppercase O, grave accent	Ò	Ò	Ò
uppercase O, acute accent	Ó	Ó	Ó
uppercase O, circumflex accent	Ô	Ô	Ô
uppercase O, tilde	Õ	Õ	Õ
uppercase O, umlaut	Ö	Ö	Ö
multiplication sign	×	×	×
uppercase O, slash	Ø	Ø	Ø
uppercase U, grave accent	Ù	Ù	Ù
uppercase U, acute accent	Ú	Ú	Ú
uppercase U, circumflex accent	Û	Û	Û
uppercase U, umlaut	Ü	Ü	Ü
uppercase Y, acute accent	Ý	Ý	Ý
uppercase THORN, Icelandic	Þ	Þ	Þ
lowercase sharps, German	ß	ß	ß
lowercase a, grave accent	à	à	à
lowercase a, acute accent	á	á	á
lowercase a, circumflex accent	â	â	â
lowercase a, tilde	ã	ã	ã
lowercase a, umlaut	ä	ä	ä
lowercase a, ring	å	å	å
lowercase ae	æ	æ	æ
lowercase c, cedilla	ç	ç	ç
lowercase e, grave accent	è	è	è
lowercase e, acute accent	é	é	é
lowercase e, circumflex accent	ê	ê	ê
lowercase e, umlaut	ë	ë	ë
lowercase i, grave accent	ì	ì	ì
lowercase i, acute accent	í	í	í
lowercase i, circumflex accent	î	î	î
lowercase i, umlaut	ï	ï	ï
lowercase eth, Icelandic	ð	ð	ð
lowercase n, tilde	ñ	ñ	ñ
lowercase o, grave accent	ò	ò	ò
lowercase o, acute accent	ó	ó	ó
lowercase o, circumflex accent	ô	ô	ô
lowercase o, tilde	õ	õ	õ
lowercase o, umlaut	ö	ö	ö
division sign	÷	÷	÷
lowercase o, slash	ø	ø	ø
lowercase u, grave accent	ù	ù	ù
lowercase u, acute accent	ú	ú	ú
lowercase u, circumflex accent	û	û	û
lowercase u, umlaut	ü	ü	ü
lowercase y, acute accent	ý	ý	ý
lowercase thorn, Icelandic	þ	þ	þ
lowercase y, umlaut	ÿ	ÿ	ÿ
Alpha	Α		Α
alpha	α		α
Beta	Β		Β
beta	β		β
Gamma	Γ		Γ
gamma	γ		γ
Delta	Δ		Δ
delta	δ		δ
Epsilon	Ε		Ε
epsilon	ε		ε
Zeta	Ζ		Ζ
zeta	ζ		ζ
Eta	Η		Η
eta	η		η
Theta	Θ		Θ
theta	θ		θ
Iota	Ι		Ι
iota	ι		ι
Kappa	Κ		Κ
kappa	κ		κ
Lambda	Λ		Λ
lambda	λ		λ
Mu	Μ		Μ
mu	μ		μ
Nu	Ν		Ν
nu	ν		ν
Xi	Ξ		Ξ
xi	ξ		ξ
Omicron	Ο		Ο
omicron	ο		ο
Pi	Π		Π
pi	π		π
Rho	Ρ		Ρ
rho	ρ		ρ
Sigma	Σ		Σ
sigma	σ		σ
Tau	Τ		Τ
tau	τ		τ
Upsilon	Υ		Υ
upsilon	υ		υ
Phi	Φ		Φ
phi	φ		φ
Chi	Χ		Χ
chi	χ		χ
Psi	Ψ		Ψ
psi	ψ		ψ
Omega	Ω		Ω
omega	ω		ω
password dot	●		●
bullet	•		•

Sunday, August 29, 2010

C++ interview questions （4）

22. what is importance of const. pointer in copy constructor?

When we try to copy one object into another using copy constructor,we need to maintain the original copy of original object (which we are copying) so while passing object we make it constant and we pass it as a by reference.

23. What is a memory leak? How can we avoid it?

A memory leak or leakage in computer science occurs when a computer program consumes memory but is unable to release it back to the operating system.
A memory leak can be avoided by making sure that whatever memory has been dynamically allocated will be cleared after the use of the same. for example

#include<iostream>
using namespace std;

void func()
{
int *a = new int; //on heap

int b; // on stack
//avoid memeory leakage
delete a; //deleting memory on heap
}

int main()
{

func();
cout<<"end of main"<<endl;
return (0);
}

24. Why always array starts with index 0?

  This boils down to the concept of Binary digits.
Take an array size of 64 for example. We start from 0 and

end at 63. We require 6 bits.But, if we were to start from

1 and end at 64, we would require 7 bits to store the

same number, thus increasing the storage size.

25 What is  stringstream? Give an example.

stringstream provides an interface to manipulate strings

as if they were input/output streams.

Members inherited from istream

istream& getline (char* s, streamsize n );
istream& getline (char* s, streamsize n, char delim );

Following is a sample program using a stringstream

to read numbers from a csv file named "input.txt" into

a 6 row by 5 column int array and
then prints the array.

It can take data from an input (text) file that

looks like this:

1,3,10,3,1
1,10,10,3,10
1,,,,
0,0,0,1,10
1,1,0,2,2
10,1,0,1,10

#include <iostream>
#include <fstream>

#include<sstream>
using namespace std;

int ROWS = 6;

int COLS = 5;
int BUFFSIZE = 80;

main() {
 int array[ROWS][COLS];
 char buff[BUFFSIZE]; // a buffer to temporarily park the data

 ifstream infile("input.txt");
 stringstream ss;
 for( int row = 0; row < ROWS; ++row ) {

   // read a full line of input into the buffer (newline is
   //  automatically discarded)
   infile.getline( buff,  BUFFSIZE );
   // copy the entire line into the stringstream

   ss << buff;
   for( int col = 0; col < COLS; ++col ) {

     // Read from ss back into the buffer.  Here, ',' is
     //  specified as the delimiter so it reads only until
     //  it reaches a comma (which is automatically
     //  discarded) or reaches the 'eof', but of course
     //  this 'eof' is really just the end of a line of the
     //  original input.  The "6" is because I figured
     //  the input numbers would be 5 digits or less.
     ss.getline( buff, 6, ',' );

     // Next, use the stdlib atoi function to convert the
     //  input value that was just read from ss to an int,
     //  and copy it into the array.
     array[row][col] = atoi( buff );
   }

   // This copies an empty string into ss, erasing the
   //  previous contents.
   ss << "";
   // This clears the 'eof' flag.  Otherwise, even after
   //  writing new data to ss we wouldn't be able to
   //  read from it.
   ss.clear();
 }

 // Now print the array to see the result
 for( int row = 0; row < ROWS; ++row ) {

   for( int col = 0; col < COLS; ++col ) {

     cout << array[row][col] << " ";
   }
   cout << endl;
 }

 infile.close();
}

server client and socket programming-C++

Server:

1)Establish a listening socket and wait for connections from clients.
2)Accept the client's connection attempt.
3)Send and receive data.
4) Close the connection.

Client:

1) Create a client socket and attempt to connect to server.
2) Send and receive data.
3) Close the connection.

File Download site
Makefile: Makefile for this project
Socket.h: define Socket class and declare server function create, bind, listen, accept client function: connect, data function send, recv
SocketException.h: define SocketException class to deal with
class method fail. If a class method fails for any reason, it throws an exception of type SocketException.
SeverSocket.h: define SeverSocket class derived from Socket class, redefine accept method and define overloaded the << and >> operators, so that when used, they wrote data to and read data from the socket.
ClientSocket.h: define ClientSocket class derived from Socket class,
define overloaded the << and >> operators, so that when used, they wrote data to and read data from the socket.
Socket.cpp, ServerSocket.cpp and Client.Socket.cpp detaily define
methods declared in header file
simple_server_main.cpp: a simple implementation of a server
The new_sock variable contains all of our socket information, so we use it to exchange data with the client. The line "new_sock >> data;" should be read as "read data from new_sock, and place that data in our string variable 'data'." Similarly, the next line sends the data in 'data' back through the socket to the client.

If you're paying attention, you'll notice that what we've created here is an echo server. Every piece of data that gets sent from the client to the server gets sent back to the client as is. We can write the client so that it sends a piece of data, and then prints out the server's response:
simple_client_main.cpp: a simple implementation of a client
We send the string "Test Message." to the server, read the response from the server, and print out the response to std output.

Saturday, August 28, 2010

C++ interview questions (3)

19. What is function template and class template?

Function templates are special functions that can operate with generic types.

template <class myType>
myType GetMax (myType a, myType b) {
 return (a>b?a:b);
}

example:

int a=GetMax(1,2);

double b=GextMax(1.0,2.0);

Class template have members that use template parameters as types

template <class T>
class mypair {
    T values [2];
  public:
    mypair (T first, T second)
    {
      values[0]=first; values[1]=second;
    }
};

Example:

mypair<int> myobject (115, 30);

mypair<double> myfloats (3.03, 2.28);

20 .What is POLYMORPHISM and give an example using eg. SHAPE object: If I have a base class SHAPE, how would I define DRAW methods for two objects CIRCLE and SQUARE

POLYMORPHISM : A phenomenon which enables an object to react differently to the same function call.
in C++ it is attained by using a keyword virtual
example
public class SHAPE
{
public virtual void SHAPE::DRAW()=0;
};
Note here the function DRAW() is pure virtual which means the derived classes must implement the DRAW() method.
public class CIRCLE::public SHAPE
{
public void CIRCLE::DRAW()
{
// TODO drawing circle
}
};
public class SQUARE::public SHAPE
{
public void SQUARE::DRAW()
{
// TODO drawing square
}
};

21. What is virtual function? Give an example to explain using/not using virtual function.

C++ virtual function is a member function of a class, whose functionality can be over-ridden in its derived classes.

#include<iostream>
using namespace std;

 class Window // Base class for C++ virtual function example
     {
       public:
          virtual void Create() // virtual function for C++ virtual function example
        //     void Create()

          {
               cout <<"Base class Window"<<endl;
          }
     };

     class CommandButton : public Window

     {
       public:
          void Create()
          {
              cout<<"Derived class Command Button - Overridden C++ virtual function"<<endl;
          }
     };

     int main()
     {
         Window  *x, *y;

         x = new Window();
         x->Create();

         y = new CommandButton();
         y->Create();
         return(0);
     }

If the function create  is declared virtual, the following output is given:

Base class Window
Derived class Command Button - Overridden C++ virtual function

If the function create is not declared virtual, the following output

is given

Base class Window

Base class Window

The base function create is kept calling.

Friday, August 27, 2010

C++ interview Questions (2)

Question 1-11 see:
C++ interview Questions (1)

12. You’re given a simple code for the class

Circle. Write the following functions:

Copy constructor
= operator overload
== operator overload
+ operator overload

Class  Circle{
    private：
          double  r;
    public:
          Circle(double r0);
          Circle(const Circle& myCircle); //copy constructor

  //= operator overload

Circle& operator=(const Circle& myCircle);

//== operator overload

int operator==(const Circle& myCircle1, const Circle& myCircle2);

//+ operator overload

Circle& operator+(const Circle& myCircle1, const Circle& myCricle2 );

};

Circle::Circle(double r0){
             r = r0;
}
Circle::Circle(const Circle& myCircle){
     this.r = myCircle.r;
}
Circle& Circle::operator=(const Circle& myCircle)

{

    r = myCircle.r;
    return *this;

}
int Circle::operator==(const Circle& myCircle1, const Circle& myCircle2)

{

    return (myCircle1==myCircle2);

}
Circle& Circle::operator+(const Circle& myCircle1, const Circle& myCircle2)

{

    r = myCircle1.r+myCircle2.r;
    return *this;

}

int main(){
      Circle FirstCircle(2.0);
      Circle SecondCircle=FirstCircle；// this invokes the copy constructor
      return 0;
}
13 What memory part is accessed when you run a program?
heap
 dynamic memory allocation (also known as heap-based memory

allocation) is the allocation of memory storage for use in 
a computer program during the runtime of that program.
Static memory allocation refers to the process of allocating

memory at compile-time before the associated program is executed.
Stacks in computing architectures are regions of memory

where data is added or removed in a last-in-first-out manner,

while heap is first-in-first-out.
stack allocation is very simple and typically faster than

heap allocatio.


14. For an empty class, what method is accessed?
default constructor, copy constructor, destructor

15. binary tree, array, hashed table, which one can be

 random accessed?
array

16. What is default constructor?
What a class is created, default constructor is automatically

called to initialize the class.


17. Which member can be accessed by a derived class?
public member and protected member.

18. What is object oriented programming? What is class and object?

What is difference between class and object?

Object-oriented programming (OOP) is a programming paradigm that uses "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. A class is a definition of an object. Object is an instance of a class.
Every object belongs to a class and every class contains one or more related objects.

18. Describe C/C++ Standard Template Library (STL).

The Standard Template Library (STL) is a software library partially included in the C++ Standard Library. It provides containers, iterators, algorithms, and functors. More specifically, the C++ Standard Library is based on the STL published by SGI.
C++ Standard Library

    * ios, iostream, iomanip, fstream, sstream

Standard Template Library

    * vector, deque, list, map, set, stack, queue, bitset, algorithm
    * functional,iterator

C Standard Library

    * cassert, cctype, cerrno,climits, clocale, cmath
    * csetjmp, csignal, cstdarg, cstddef
    * cstdio, cstdint, cstdlib, cstring, ctime

My pipe job list

I create several job lists using yahoo pipe:

1. computer job in Vancouver
2. Physics jobs in Canada
3. University and college jobs near Vancouver

Thursday, August 26, 2010

Create a thread in C/C++

A thread of execution is the smallest unit of processing that can be scheduled by an operating system. It generally results from a fork of a computer program into two or more concurrently running tasks.

The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.
compile:
g++ -lpthread thread.c

thread.c as following

-----------------------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *print_message( void *ptr )
{
   printf("%s \n", (char*) ptr);
}
int main()
{
     pthread_t thread1;
     char *m = "Thread 1";
     int  iret1;
    /* Create a  thread each to execute function */
    /* message1 pass to function print_message*/

iret1 = pthread_create( &thread1, NULL, print_message, (void*) m);
     /* pthread_join - wait for termination of another thread*/
     pthread_join( thread1, NULL);

     printf("Thread 1 returns: %d\n",iret1);

     return(0);

}

 ------------------------------------------------

 Pipes can be used in threads and processes. The program below
demonstrates how pipes can be used in processes. A new process can be
created using the system call fork(). It returns two differnt values to
the child and parent. The value 0 is returned to the child (new)
process and the PID (Process ID) of the child is returned to the parent
process. This is used to distinguish between the two processes. In the
program given below, the child process waits for the user input and
once an input is entered, it writes into the pipe. And the parent
process reads from the pipe.

Note here that the pipe() system call was called before the system call fork(). The buffer allocated to the pipe is accessible to both the processes.

g++ pipe_test.c

below is pipe_test.c

#include <stdlib.h>
#include <stdio.h>

#include <unistd.h>

/* Write COUNT copies of MESSAGE to STREAM, pausing for a second
   between each.  */

void writer (const char* message, int count, FILE* stream)
{

  for (; count > 0; --count) {
    /* Write the message to the stream, and send it off immediately.  */
    fprintf (stream, "%s\n", message);

    fflush (stream);
    /* Snooze a while.  */
    sleep (1);
  }
}

/* Read random strings from the stream as long as possible.  */

void reader (FILE* stream)
{
  char buffer[1024];

  /* Read until we hit the end of the stream.  fgets reads until
     either a newline or the end-of-file.  */
  while (!feof (stream) 
  && !ferror (stream) 
  && fgets (buffer, sizeof (buffer), stream) != NULL) 
    fputs (buffer, stdout);
}

int main ()
{
  int fds[2];
  pid_t pid;

  /* Create a pipe.  File descriptors for the two ends of the pipe are
     placed in fds.  */
  pipe (fds);
  /* Fork a child process.  */
  pid = fork ();

  if (pid == (pid_t) 0) {
    FILE* stream;

    /* This is the child process.  Close our copy of the write end of
       the file descriptor.  */
    close (fds[1]);
    /* Convert the read file descriptor to a FILE object, and read
       from it.  */
    stream = fdopen (fds[0], "r");

    reader (stream);
    close (fds[0]);
  }
  else {

    /* This is the parent process.  */
    FILE* stream;
    /* Close our copy of the read end of the file descriptor.  */
    close (fds[0]);

    /* Convert the write file descriptor to a FILE object, and write
       to it.  */
    stream = fdopen (fds[1], "w");

    writer ("Hello, world.", 5, stream);
    close (fds[1]);
  }

  return 0;
}

Wednesday, August 25, 2010

statistics analysis in Matlab

1) Mode:
The mode of a data sample is the element that occurs most often in the collection.

x=[1 2 3 3 3 4 4]

mode(x) % return 3, happen most

2)Median:
a median is described as the numeric value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to highest value and picking the middle one

median(x) % return 3

3) mean
Total sum divided by number of values

mean(x) % return 2.8571

4) quartile
first quartile (25th percentile)
second quartile (50th percentile)
third quartile (75th percentile)
kth percentile

prctile(x, 25) % 25th percentile, return 2.25

prctile(x, 50) % 50th percentile, return 3, i.e. median

5) skewness
Skewness is a measure of the asymmetry of the data around the sample mean. If skewness is negative, the data are spread out more to the left of the mean than to the right. If skewness is positive, the data are spread out more to the right.

skewness(x) % return-0.5954

6)kurtosis
Kurtosis is a measure of how outlier-prone a distribution is.

kurtosis(x) % return2.3594

7) Standard deviation
the square root of an unbiased estimator of the variance of the population from which X is drawn, as long as X consists of independent, identically distributed samples.

std(x) %return 1.0690

8) Variance
describes how far values lie from the mean

var(x) %return 1.1429

9) moment
a quantitative measure of the shape of a set of points.

moment(x, 2); %return second moment

10. covariance
measure of how much two variables change together

y2=[1 3 4 5 6 7 8]

cov(x,y2) %return 2*2 matrix, diagonal represents variance

11.Linear Regression:
modeling the relationship between a scalar variable y and one or more variables denoted X. In linear regression, models of the unknown parameters are estimated from the data using linear functions.

polyfit( x,y2,1) %return 2.1667 -1.3333, i.e 2.1667x-1.3333

12. One sample t-test
A t-test is any statistical hypothesis test in which the test statistic follows a Student's t distribution if the null hypothesis is supported.

[h,p,ci] = ttest(y2,0)% return 1 0.0018 ci =2.6280 7.0863

This time the test rejects the null hypothesis at the default α = 0.05 significance level. The p value has fallen below α = 0.05 and the 95% confidence interval on the mean does not contain 0.
Because the p value of the sample y is greater than 0.01, the test will fail to reject the null hypothesis when the significance level is lowered to α = 0.01:

Tuesday, August 24, 2010

Jobs in Vancouver in Science & Technology

360networks Corporation
Accenture Business Services Of British Columbia Limited
Aldrichpears Associates Ltd.
Amec Inc.
Biopharmaceutical Research Inc
Blast Radius Inc.
Canwel Distribution Ltd.
Cavendish Analytical Laboratory Ltd.
Citizens Bank Of Canada
Cochrane Group, The
David Suzuki Foundation
Dental Technologies Inc.
E-Atelier Architecture Inc.
Emergency Communications For Southwest British Columbia Inc.
Evs Environment Consultants Ltd.
Gage-Babcock & Associates Ltd.
Genome Sciences Centre
Hatch Ltd.
Intel Of Canada, Ltd.
Iti International Technology Integration Inc
Kerr Wood Leidal Associates Ltd.
Kinexus Bioinformatics Corp.
Klohn Crippen
Ledcor Industries Inc
Lexmark Canada Inc
Lmdg Building Code Consultants Ltd.
Make Technologies, Inc
Nd Lea Consultants Ltd
Netnation Communications, Inc
Neuromed Technologies Inc
Ngrain Corporation
Oncogenex Technologies Inc.
Pacific Business & Law Institute
Radiant Communications Corp.
Rainmaker Limited Partnership
Relic Entertainment Inc
Rescan Environmental Services Ltd
Rsa Security Inc
Sandwell Engineering Inc.
Selkirk Financial Technologies, Inc.
Sierra Systems Group Inc.
Skeans Engineering And Machinery Ltd.
Snc-Lavalin Inc.
Sporg Internet Corp.
Stantec Inc
Stemcell Technologies Inc
Syreon Corporation
Terasen Gas
Urs Norelco Dames & Moore Inc.
Vancouver Aquarium Marine Science Centre
Vancouver Hospital And Health Sciences Centre
Vision Critical Communications Inc.
http://www.jobboardvancouver.com/

Cold call in job search

A cold call is a very effective way for searching hidden job market.
The goal of cold call is to lead to a job interview.
But a lot of people don't use cold call because:

It's scary to do

It uses scripted, forced conversations that sound like a sales pitch

The fear of being rejected or not knowing what to say

In cold call, followings steps to follow:
1) Introduction: "Hi, I am Jiansen Lu"
2) Give a brief explanation of your work background and your level of experience. ie. "I'm a software programmer with 10 years experience. Can I talk to the hiring manager
to enquire the job opportunity in your company?"
3)Finally ask for an interview. ie. "When can I meet with you in person"
I use goolg map to search
"IT company in Vancouver" and start cold calls.
1) PrimeObects, tel:Vancover, BC Canada
+1 (604) 807-7068(General inquiry)
result: voicemail
2) PCIS career (recruiter)

Monday, August 23, 2010

C++ company directory in Vancouver

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