/*************************************************************************/

/*									 */

/*  Statistical routines for C4.5					 */

/*  -----------------------------					 */

/*									 */

/*************************************************************************/





#include "defns.i"

#include "types.i"

#include "extern.i"



									

/*************************************************************************/

/*									 */

/*  Compute the additional errors if the error rate increases to the	 */

/*  upper limit of the confidence level.  The coefficient is the	 */

/*  square of the number of standard deviations corresponding to the	 */

/*  selected confidence level.  (Taken from Documenta Geigy Scientific	 */

/*  Tables (Sixth Edition), p185 (with modifications).)			 */

/*									 */

/*************************************************************************/





float Val[] = {  0,  0.001, 0.005, 0.01, 0.05, 0.10, 0.20, 0.40, 1.00},

      Dev[] = {4.0,  3.09,  2.58,  2.33, 1.65, 1.28, 0.84, 0.25, 0.00};





float AddErrs(N, e)

/*    -------  */

    ItemCount N, e;

{

    static float Coeff=0;

    float Val0, Pr;



    if ( ! Coeff )

    {

	/*  Compute and retain the coefficient value, interpolating from

	    the values in Val and Dev  */



	int i;



	i = 0;

	while ( CF > Val[i] ) i++;



	Coeff = Dev[i-1] +

		  (Dev[i] - Dev[i-1]) * (CF - Val[i-1]) /(Val[i] - Val[i-1]);

	Coeff = Coeff * Coeff;

    }



    if ( e < 1E-6 )

    {

	return N * (1 - exp(log(CF) / N));

    }

    else

    if ( e < 0.9999 )

    {

	Val0 = N * (1 - exp(log(CF) / N));

	return Val0 + e * (AddErrs(N, 1.0) - Val0);

    }

    else

    if ( e + 0.5 >= N )

    {

	return 0.67 * (N - e);

    }

    else

    {

	Pr = (e + 0.5 + Coeff/2

	        + sqrt(Coeff * ((e + 0.5) * (1 - (e + 0.5)/N) + Coeff/4)) )

             / (N + Coeff);

	return (N * Pr - e);

    }

}