FUNCTION PT(N,X)
C WAHRSCHEINLICHKEIT VON ST(N) = X
C ST = STUDENT-VERTEILUNG
C  N = FREIHEITSGRADE
C NACH DECUS NO. FOCAL 8-308
C FORTRAN II
	X=X*X+.1E-15
	ID=2*(N/2)-N+2
	W=X/FLOAT(N)
	Z=1./(1.+W)
	IF(ID-1)1000,1001,1000
1000	PT=SQRT(W*Z)
	D=.5*PT*Z/W
	GOTO 1002
1001	PT=SQRT(W)
	Y=.31830989
	D=Y*Z/PT
	PT=2.*Y*ATAN(PT)
1002	Y=2.*W/Z
	J=ID+2
1003	IF(J-N)1004,1004,1005
1004	D=D*Z*(1.+1./FLOAT(J-2))
	PT=PT+D*Y/FLOAT(J-1)
	J=J+2
	GOTO 1003
1005	RETURN
	END