C / C++ / MFC

Re: how to implement three indepedent random number generators in the same subroutine/function

9-Apr-10 17:34

I am using c++. In one method (subroutine) I need to implement three independent random number generators. I do not know how to isolate them from each other. I am using a subroutine ran1(ikum) from Numerical Recipes. I other words, the seed of the random generator must be independent.

Thanks

Adam Roderick J9-Apr-10 18:09

Re: how to implement three indepedent random number generators in the same subroutine/function

9-Apr-10 18:09

Here it is Smile | :)

int rand1()
{
srand(time(NULL));
return rand() % 100 + 11;
}

Now similarly u can create a few other one srand(time(NULL)) will generate different sequence on startup.
Just refer
http://www.cplusplus.com/reference/clibrary/cstdlib/rand/

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mrby1239-Apr-10 18:25

Re: how to implement three indepedent random number generators in the same subroutine/function

9-Apr-10 18:25

Thanks a lot.

In fact, I have to generate three indenpendent random numbers with the same for loop.

For (int i=0;i

Adam Roderick J9-Apr-10 19:23

Re: how to implement three indepedent random number generators in the same subroutine/function [modified]

9-Apr-10 19:23

Just check this.
int rand1( int nData)
{
return rand() % 100 + nData;
}
int main(int argc, char *argv[])
{
int Temp;
srand(time(NULL));
for( int i = 0; i< 11; i++)
{
Temp = rand1(1) ;
cout<<"Num1=="<<temp<<endl;
temp="rand1(2);
" cout<<"num2="="<<Temp<<endl;
" cout<<"num3="="<<Temp<<endl;
" }
="" return="" 0;
}
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mrby1239-Apr-10 19:40

Re: how to implement three indepedent random number generators in the same subroutine/function

9-Apr-10 19:40

Thanks.

I am using a different random number generator which generates a normal distribution of a random number generator - N(0,1). This function is from a book called: Numerical Recipes.

When I call it, I call gasdev(int &idum); For example: t=time[i]+sd_error*gasdev(int &idum);
In one subroutine, I need to call gasdev(int &idum) three times, but I want each time it is independent.

int idum1=-1;
int idum2=-1;
int idum3=-1;
//
date=time[i]+t_sd_error*gasdev(idum1);
money=t_sd_error*gasdev(idum2);
force=force_sd_error*gasdev(idum3);

date, money, and force are totally independent variables. Do you think I am OK to make the three calls independent with above idum1, idum2, and idum3 ?

Here is it:

//
double C_procDlg::ran1(int &idum)
{
const int IA=16807,IM=2147483647,IQ=127773,IR=2836,NTAB=32;
const int NDIV=(1+(IM-1)/NTAB);
const double EPS=3.0e-16,AM=1.0/IM,RNMX=(1.0-EPS);
static int iy=0;
static int iv[100];
int j,k;
double temp;

if (idum<=0||!iy) { //initialize
if(-idum<1) idum=1;
else idum=-idum;
for(j=NTAB+7;j>=0;j--){
k=idum/IQ;
idum=IA*(idum-k*IQ)-IR*k;
if(idum<0) idum+=IM;
if(j<NTAB) iv[j]=idum;
//
}
iy=iv[0];
}
k=idum/IQ;
idum=IA*(idum-k*IQ)-IR*k;
if (idum<0) idum+=IM;
j=iy/NDIV;
iy=iv[j];
iv[j]=idum;
if((temp=AM*iy)>RNMX) return RNMX;
else return temp;
}
//
double CBlast_vib_procDlg::gasdev(int &idum)
{
static int iset=0;
static double gset;
double fac,rsq,v1,v2;
//
if(idum<0) iset=0;
if (iset==0){
do{
v1=2.0*ran1(idum)-1.0;
v2=2.0*ran1(idum)-1.0;
//
rsq=v1*v1+v2*v2;
}
while(rsq>=1.0||rsq==0.0);
fac=sqrt(-2.0*log(rsq)/rsq);
gset=v1*fac;
iset=1;
return v2*fac;
}
else{iset=0;
return gset;
}}

modified on Saturday, April 10, 2010 1:58 AM

mrby12310-Apr-10 19:34

Re: how to implement three indepedent random number generators in the same subroutine/function

10-Apr-10 19:34

What do you think if I use your above code to generate three seeds for my three random number generators?

My aim is to generate three random number sequence which are totally un-correlated each time to run the program?

Thanks

Adam Roderick J10-Apr-10 20:52

Re: how to implement three indepedent random number generators in the same subroutine/function

10-Apr-10 20:52

I believe this logic surely generate new sequences, but remember that

rand() % X + nData;

If the value si X is bigger then there is less chances that the same number is repeated.

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mrby12314-Apr-10 7:21

Re: how to implement three indepedent random number generators in the same subroutine/function

14-Apr-10 7:21

Thanks. I like you to do more comments. What you suggest ?

mrby12314-Apr-10 7:20

post mouse move, wheel, RClick messages, (captured by CView) to the started thread

14-Apr-10 7:20

Thanks. Your above code works. I will use it to generate seeds for a generator of a normal distribution diviates

m_code9-Apr-10 11:46

m_code

9-Apr-10 11:46

Hi, I created a thread in CView::OnInitialUpdate method of my CView class now I want to know how could I post my mouse move, wheel, RClick messages, (captured by CView) to the started thread, I have saved my thread pointer in m_pThread datamember.

a simple code would make the case more clear to me,
Regards

Re: post mouse move, wheel, RClick messages, (captured by CView) to the started thread

Adam Roderick J9-Apr-10 18:11

Re: post mouse move, wheel, RClick messages, (captured by CView) to the started thread

9-Apr-10 18:11

PostThreadMessage is the one you are looking for http://msdn.microsoft.com/en-us/library/ms644946(VS.85).aspx

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m_code9-Apr-10 18:43

m_code

9-Apr-10 18:43

Thank you,
But what do I put to the the third and 4th arguments?

BOOL CMyView::OnMouseWheel(UINT nFlags, short zDelta, CPoint pt)
{
	::PostThreadMessage(m_pThread->m_nThreadID, WM_MOUSEWHEEL, ???, ???);

	return CView::OnMouseWheel(nFlags, zDelta, pt);
}

Re: post mouse move, wheel, RClick messages, (captured by CView) to the started thread

Adam Roderick J9-Apr-10 19:12

C++ class hierarchy design problem

9-Apr-10 19:12

Use MAKELPARAM and MAKEWPARAM to set the delta and point. as the next parameters.

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kylur9-Apr-10 9:00

9-Apr-10 9:00

Fellow coders,

RE: a C++ design problem.

I am attempting to construct a C++ class hierarchy on top of a C legacy system. The result
will be then placed into an embedded controller. The controller communicates with a Windows
program via a series of 'software pipes' to a supplied DLL and then calls in the Windows
program to fetch information from the DLL. The data in a given pipe will be of a specific type.

In order to generalize this process the third party library uses the following header:

typedef unsigned char BYTE;
typedef unsigned short WORD;
typedef unsigned long DWORD;

typedef union gen_scalar {
    double  _double;
    __int64 _i64;
    float   _float;
    long    _i32;
    short   _i16;
    DWORD   _long;
    WORD    _word;
    BYTE    _byte;
} GENERIC_SCALAR;

And then, for example, reading a long from a pipe would be:

long Get(PIPE* pipe)
{
    GENERIC_SCALAR v;
    pipe_value_get(pipe, &v);
    Return v._i32;
};

So, the hierarchy starts with a base class:

class Pipe
{
public:
    Pipe(PIPE* pipe)
        : pipe_(pipe)
    {};
    virtual ~Pipe()
    {};

protected:
    PIPE*   pipe_;
};

where a PIPE* is just a handle to the communication pipe.

Then an input class is needed:

class IPipe : public Pipe
{
public:
    IPipe(PIPE* pipe)
        : Pipe(pipe)
    {
        pipe_open(pipe_, P_READ);
    };
};

There would also be a corresponding output class OPipe.

And now the part I need help with!

Suppose I know a pipe will contain a series of 'shorts'. Then I could create:

class ShortIPipe : public IPipe
{
public:
    ShortIPipe(IPIPE* pipe)
        : IPipe(pipe)
    {};

    short Get() const
    {
        GENERIC_SCALAR v;
        pipe_value_get(pipe_, &v);
        return v._i16;
    };
};

And so on for a long, double, float, etc, pipe(s).

However, the only difference between all these classes is the return value, that is,
v._i16 or v._i32, etc.

I'd prefer to create a single class which can handle them all. Maybe a template class?
For example:

template <typename T>
class IPipe : public Pipe
{
public:
    IPipe(PIPE* pipe)
        : Pipe(pipe)
    {
        pipe_open(pipe_, P_READ);
    };


    T Get() const
    {
        GENERIC_SCALAR v;
        pipe_value_get(pipe_, &v);
        return v._???;// depends on T
    };
};

Used like:

IPipe<short> spipe(...);
short s = spipe.Get();

And so, (finally) the question is how, within the Get() member, do I define the return value?
Note: the embedded controller cannot support RTTI. And I'd prefer not to have a big switch.

Any help would be much appreciated!
Kylur.

Jonathan Davies9-Apr-10 10:28

Jonathan Davies

9-Apr-10 10:28

How about Template specialization?

template<> class IPipe<short>
{
...
    return v._i16;
...
}
template class IPipe<long>
{
...
    return v._i32;
....
}

kylur12-Apr-10 9:47

12-Apr-10 9:47

Thanks for the reply, Jonathan.

Yes, this works - if fact it was my original attempt! I rejected it only because it just looked too wordy - I know, bad reason but I've got a little extra time to do investigations on this project so I thought I'd try a few other ideas.

Regards,
Kylur.

Bernódus Kristinsson9-Apr-10 11:04

Bernódus Kristinsson

9-Apr-10 11:04

template<typename T> T 
get_the_value(gen_scalar const& gs) const;// primary template no need for definition

template<double> inline double 
get_the_value(gen_scalar const& gs) const { return gs._double; }

template<short> short inline 
get_the_value(gen_scalar const& gs) const { return gs._i16; }


//... and so on for all types in the union (never remember the placement of inline)


template<typename T>
class IPipe : public Pipe
{
public:
	IPipe(PIPE* pipe) : Pipe(pipe) { pipe_open(pipe_, P_READ); };

	T Get() const
	{
		GENERIC_SCALAR v;
		pipe_value_get(pipe_, &v);
		return get_the_value<T>(v);// important:  <T>
	};
};


// several small functions instead of same number of classes

kylur12-Apr-10 10:25

12-Apr-10 10:25

Thank you for the reply, Berndus.

This answer really caught my eye as it 1) took advantage on templates and specialization, 2) the helper functions can all be moved into the IPipe class as private members, 3) is understandable and 4) is short.

Looking closer at the get_the_value functions and they start to look very similar to the reinterpret_cast as suggested in another reply - the only difference being explicitly returning the union member.

Good job! I think this is the solution I'll use.

Regards,
Kylur.
Smile | :)

cmk9-Apr-10 14:52

cmk

9-Apr-10 14:52

Did you try: return (T&)v;

...cmk

The idea that I can be presented with a problem, set out to logically solve it with the tools at hand, and wind up with a program that could not be legally used because someone else followed the same logical steps some years ago and filed for a patent on it is horrifying.
- John Carmack

kylur12-Apr-10 10:09

12-Apr-10 10:09

Thanks for the reply, "cmk".

And no I had not tried your suggestion.
But now I (almost) have (I used return reinterpret_cast<t&>(v);) and yes it does work! And I'm not sure if you're a friggin' genius or if I'm just an idiot for not seeing this solution.

For some unknown reason however, I'm a little reluctant to use this - "gurus" tend to frown on casts and in this case I'm not really sure what a reinterpret_cast of a union is really doing (although I have to say it does seem to work).

I'll really have to think about this some more!

Regards,
Kylur.

cmk12-Apr-10 12:45

cmk

12-Apr-10 12:45

20 yrs of C++, more for C.
There is NOTHING wrong with using the (T&) cast.