Undefined reference to ln() and ranf()

**vbdave78** · 03-03-2009

Hi,

I am trying to generate gaussian random variables. I am using the following snippet of code to do this. However it gives me the error "undefined reference to ln()". It does the same for ranf(). have included math.h in my header file. It doesnt give me an error for sqrt() because I use the option -lm at command prompt when I compile. This is my first time trying to use these scientific functions. Any help would be appreciated.
Thanks

Code:

 for(k=0;k<(N+1);k+2)
    {
      do 
	{
	  x1 = 2.0 * ranf() - 1.0;
	  x2 = 2.0 * ranf() - 1.0;
	  w = x1 * x2 + x2 * x2;
	} while(w >= 1.0);
      w = sqrt((-2.0 * ln(w))/w);
      x[k] = x1 * w;
      x[k+1] = x2 * w;
    }

**laserlight** · 03-03-2009

Post the smallest and simplest program that demonstrates the error. Note that ranf() and ln() are not part of the C standard library.

**vbdave78** · 03-03-2009

Here is a simple program that I ran using the following command
cc error.c -lm.
I am running this code on a linux machine.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
main()
{
  float x1, x2, w, y1, y2; /* Variables used to generate random values */
  int k;
  double x[10];
  int N = 6;
  for(k=0;k<(N+1);k+2)
    {
      do 
	{
	  x1 = 2.0 * ranf() - 1.0;
	  x2 = 2.0 * ranf() - 1.0;
	  w = x1 * x2 + x2 * x2;
	} while(w >= 1.0);
      w = sqrt((-2.0 * ln(w))/w);
      x[k] = x1 * w;
      x[k+1] = x2 * w;
      printf("%lf",x[k]);
    }
}

**laserlight** · 03-03-2009

Where is ranf() and ln() defined? As I mentioned, they are not part of the C standard library (and probably not provided as a compiler extension), so including <math.h> and specifying -lm is of no use except for sqrt().

**tabstop** · 03-03-2009

So what normal people call "ln" C calls "log". And if you want ranf, you have to write it yourself, or link in the code that has it in it.

**vbdave78** · 03-03-2009

Thank you for your help.
I have figured out that I need the GSL header files to be able to use those functions. I cant find them on my system anywere however which is a different story all together. But thanks for your input.

**hk_mp5kpdw** · 03-03-2009

Just having the headers isn't going to help, you'll need some type of code library to link to as well (one that goes along with the headers you mention).

Thread: Undefined reference to ln() and ranf()

Thread Tools

Search Thread

Display

Undefined reference to ln() and ranf()

Tags for this Thread