about lock - C# Discussion Boards

Re: Pre-Build events for specific configurations

6-Oct-03 9:21

use the ol' empty C++ project trick Smile | :)

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Joe Woodbury6-Oct-03 9:39

Joe Woodbury

6-Oct-03 9:39

Good idea. Thanks.

Joe Woodbury

When all else fails, there's always delusion.
- Conan O'Brien

Statistical Functions in C#

AZBugsBunny6-Oct-03 8:00

AZBugsBunny

6-Oct-03 8:00

I would like to know if there is any built in function/library in C# which lets me solve the foll. Statistical problem:
Given the mean and the variance of a normal distribution, I want to get the sample points that are arrived at based on the mean and variance.
(Basically some function similar to the Worksheet function NormInv in MSExcel).
Right now I am doing a very kludgy solution where I create an Excel Worksheet function object just to access the function. This makes my application real slow. Frown | :(

Moreover I need this type of evaluation to be done possibly 10,000 times as I am developing some kind of a simulator.
Anybody please help !!!!

leppie6-Oct-03 9:28

6-Oct-03 9:28

Those methods wouldnt be hard at all to implement in a class or two. In fact thats a good idea for your 1st article here at CodeProject. Smile | :)

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Kevin McFarlane6-Oct-03 10:37

Kevin McFarlane

6-Oct-03 10:37

I'm sure I remember there being a C# math library on the web somewhere - probably not free though and I can't remember what it was called or whether it supported stats.

Ah, just did a search and there's one here: http://www.centerspace.net/products.php?page=3[^]

The stats library is released next month.

Kevin

leppie6-Oct-03 12:31

6-Oct-03 12:31

Now that kevin mentioned it. Do a search for Math.NET and Euler.NET on SOurceforge, both provide stats functions i think.

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Donald_a8-Oct-03 3:40

Donald_a

8-Oct-03 3:40

I'm not sure exactly what you are after, but this may help?

using System;

namespace NormInvFunc{

	public class Normal
	{         
	        private static double Density(double x)
		{
			double y=Math.Pow (2*Math.PI ,-.5)*Math.Exp(-.5*x*x);
			return y;
		}

		public static double StandardNormal(double x)
		{
			double [] a=new double[5];
			a[0]=.31938153;
			a[1]=-.356563782;
			a[2]=1.781477937;
			a[3]=-1.821255978;
			a[4]=1.330274429;
 
			double K=.2316419;
			double L=Math.Abs(x);
			double nx=Density(L);
			double q=1/(1+K*L);
			double S=0;
			for(int j=0;j<5;j++)
			{
				S+= a[j]*Math.Pow(q,j+1);
			}
			double SND=1-nx*S;
			if(x<0)
			{
				SND=1-SND;
			}
			return SND;
 
		}
                                                               
		public static double StandardNormalInv(double R)
		{
			double Delta=1;
			double X=0;
			double Y=0;
			do
			{
				Y=X-(StandardNormal(X)-R)/Density(X);
				Delta=Math.Abs (Y-X);
				X=Y;
			}
			while (Delta>.000000001);
 
			return Y;
 		}
 
	}
 
}

NB will not return quite as many decimal places as excel.

about lock

yyf6-Oct-03 5:52

yyf

6-Oct-03 5:52

I am try to use multi-thread. I use "lock" like this:

class MyClass<br />
{<br />
  private object status = null; <br />
<br />
<br />
  myfun() {<br />
   ...<br />
   lock ( status ) {<br />
     status = new object(1);<br />
   }<br />
   ...<br />
  }<br />
}

But it gave me an "ArgumentNullException", anyone know why?

Thanks in advance.

jparsons6-Oct-03 6:21

6-Oct-03 6:21

You need an actual object to lock.
yyf wrote:
private object status = null

Change line into

private object status = new object()<br />
<br />
And everything will be happy.  But then again I'm not sure why you're trying to create the object inside of the lock.  <br />
<br />
Jared <br />
<a>jparsons@jparsons.org</a><br />
<a href="http://www.prism.gatech.edu/~gte477n">www.prism.gatech.edu/~gte477n</a>

Help me dominate the world - click this link and my army will grow

Daniel Turini6-Oct-03 6:30

Daniel Turini

6-Oct-03 6:30

Maybe he's trying to make a late initialization for some reason, and wants to prevent it to be initialized two times. If that's the case, what he needs is a second variable to protect the access to status, or initializing it the way you described.

jparsons6-Oct-03 6:36

6-Oct-03 6:36

Or he can just use a static constructor.

Jared
jparsons@jparsons.org
www.prism.gatech.edu/~gte477n

yyf6-Oct-03 7:39

yyf

6-Oct-03 7:39

Thanks for all your response. Sorry, I didn't make myself clear.

Actually I want to change the value of status in the lock block. I need to lock it in case some one else are using it.

so it should be something like that:

class MyClass<br />
{<br />
<br />
private object status = null;<br />
private object status0 = new object(0);<br />
private object status1 = new object(1);<br />
private object status2 = new object(2);<br />
<br />
myfunc()<br />
{<br />
...<br />
lock ( status ) {<br />
status = status1;<br />
}<br />
...<br />
}<br />
<br />
}

It has problem as I mentioned.

Maybe I should change it to:

status = new object(0);<br />
lock ( status )<br />
{<br />
status = status1;<br />
}

Another quick question:
From the help in .Net, it suggests I can use either this or typeof(class). But I don't understand how to use "typeof(class)"; I tried "lock ( this )", it worked. But I wonder how about if I have different variables in one class to protect. If I use "lock (this)", it'll bring up some unnecessary blocks. Right? So what should I do in this case?

Thank you very much.

jparsons6-Oct-03 13:02

6-Oct-03 13:02

yyf wrote:
1: status = new object(0);
2: lock ( status )
3: {
4: status = status1;
5: }

I've added line numbers for clarification

This function will not work as you expect it to. For example assume I have two instances of MyClass m1 and m2. Each are created in a seperate thread. m1 executes lines 1-4 and then there is a thread switch. The problem is now the lock is on the previous object status pointed to and there is virtually no way to retrieve that object. Now m2 comes along and executes line 1 and 2. It is locking a completely new object so even though the thread containing m1 is currently inside the lock, the thread containing m2 will proceed into the code block. Now event though status1 will be set correctly in your case, the code is misleading and incorrect.

The easier way to do this is through a property and a locking object.

<br />
public class MyClass<br />
{<br />
  private static object Sync = new object();<br />
  public static object _status = null;<br />
<br />
  public static object status<br />
  {<br />
    get <br />
    {  <br />
      lock ( Sync )<br />
      { <br />
        if ( _status == null ) <br />
        { <br />
          _status = new object();<br />
        }<br />
      }<br />
      return _status;<br />
    }<br />
   }<br />
   /* Rest of Class */<br />
}<br />

Or you can just use a static constructor.

Jared
jparsons@jparsons.org
www.prism.gatech.edu/~gte477n

A datatype/some way for 256 bit values?

yyf7-Oct-03 6:03

yyf

7-Oct-03 6:03

Thanks Jared, your answer are great.

However, I think it's not exactly what I want to do.

Look, in my case, the status is used as a signal in one instance. In your example, the status is used for all the instances, so you make it "static".

I usually read the code like that:

lock (this)<br />
{<br />
.....<br />
}

I think this is something similar to my case. Also if you read the help from C#.Net about the lock keyword, it said:
lock(expression) statement_block
expression
Specifies the object that you want to lock on. expression must be a reference type.
Typically, expression will either be this, if you want to protect an instance variable, or typeof(class), if you want to protect a static variable (or if the critical section occurs in a static method in the given class).

But I don't understand why I can not lock the variable which I want to protect. If I use this, how about two not related variables which I want to protect? When I lock "this" for "status", then another not related variable, let say "flag", it can not be changed either. It doesn't make sense.

Thanks again.

Fang@Illusion6-Oct-03 5:42

Fang@Illusion

6-Oct-03 5:42

Hello!

I'm kind of new to the world of C# and have a little query...Is there some way to manipulate/store/use 256 bit int/float/long so that finally a calculator for those 256 bit values can be made? I know theres the decimal datatype for 128 bits so is there a way for 256 bits too? I have got a vague idea about using a link list and that many byte nodes but are there any other means?

Thanks beforehand for time and help...

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Daniel Turini6-Oct-03 6:37

Daniel Turini

6-Oct-03 6:37

I hope this helps...
http://www.codeproject.com/csharp/BigInteger.asp

Fang@Illusion6-Oct-03 7:55

Fang@Illusion

6-Oct-03 7:55

Thankyou I have seen/have this Smile | :)

...

leppie6-Oct-03 7:06

6-Oct-03 7:06

Use a BitVector or BitArray. There really need to be better class of this.

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jparsons6-Oct-03 5:42

6-Oct-03 5:42

You could create a struct with 4 longs as private member or 2 decimals if they are 128 bits. Then you can just do the math yourself and overload all of the appropriate operators.

Jared
jparsons@jparsons.org
www.prism.gatech.edu/~gte477n