/*    function to compute inverse of students t   */
/*    Uses routine pst_ to compute students t and Numerical recipes routine */
/*    zbrent to solve for inverse          */

/*	Parameters   *q = 2 sided confidence level probability    */
/*                   *v = Degrees of freedom                     */
/*	Value returned is t such that prob(abs(t)>q)             */

/*	Limitations: Correct to within 1e-5 (zbrent tol) and will only  */
/*		     return solutions between 0 and 100    */

/* global variables that are parameters passed to function  */
double ql,vl;

double psti_(q,v)
double *q,*v;
{
	double fpsti();
	double zbrent();
        ql= *q;
	vl= *v;
/*	printf("%g %g\n",ql,vl);  */
        return zbrent(fpsti,0.,100.,1.0e-5);
}
/*	function to pass to zbrent for psti    */
double fpsti(t)
double t;
{
	double pst();	
	return pst(&t,&vl)-1.+(ql);
}

/*   function to compute students t   */
/*   Uses Numerical Recipes routine betai   */
/*   Based on numerical recipes equation 6.3.9 (p181)   */

/*   	Parameters	*t = Students t Abssicia */
/* 			*v = Degrees of freedom  */
/*	Value returned is prob(abs(t)>q) 	 */

double pst(t,v)
double *t,*v;
{

	double betai();
        return 1.-betai((*v)/2., 0.5, (*v)/((*v)+(*t)*(*t)));
}