proc format; value Xlab -1 = "-1" 0 = " 0" 1 = " 1" 
4 = "-1" 5 = " 0" 6 = " 1" 9 = "-1" 10 = " 0" 11 = " 1" other=" ";  
DATA A;
   PI2 = 8*ATAN(1); 
   DO T = 1 TO 36 BY .1; INT=.; 
      S1=SIN(PI2*T/36); S2=5+SIN(2*PI2*T/36); S3=10+SIN(3*PI2*T/36); 
      C1=2.5+COS(PI2*T/36); C2=7.5+COS(2*PI2*T/36);
      C3=12.5+COS(3*PI2*T/36);
      SS1=.; SS2=.; SS3=.; CC1=.; CC2=.; CC3=.; 
      IF ABS(T-ROUND(T))<.0001 THEN DO; 
      INT=-1.5; SS1=S1; SS2=S2; SS3=S3; CC1=C1; CC2=C2; CC3=C3; 
   END;  
   OUTPUT;
   END; 
RUN;
PROC GPLOT DATA=A; 
   AXIS1 ORDER=40 TO 0 BY -5; 
   PLOT T*(S1--C3 SS1--CC3 INT)/OVERLAY VAXIS=AXIS1 HMINOR=0 VMINOR=0
                                HREF = 0 2.5 5 7.5 10 12.5; 
   format s1 xlab.  ;
   label S1 = "X(t)";
   SYMBOL1 V=NONE I=SPLINE w= 3 C=BLACK R=6; 
   SYMBOL2 V=DOT I=NONE C=BLACK R=7; 
   TITLE "X MATRIX OF WAVES"; 
RUN; 
QUIT;

goptions reset=all; 
title " "; footnote " "; 
Data Nyquist; pi = 4*atan(1); label X = "frequency";
X=0; Y=0; output; X=pi; Y=0; output; 
Do fold = 1 to 5; 
Angle = fold*pi/36; X=X-pi*cos(Angle/2); Y = Y + pi*sin(Angle/2); 
output; X = X+pi*cos(Angle/2); Y = Y + pi*sin(Angle/2); output; 
end; 
proc format; value blank low-high = " "; 
proc gplot; plot Y*X/vaxis = 0 to 4 vminor=0 haxis=0 to 3.2 by .8; format Y blank.;
symbol1 v=none i=join c=black w=2; 
run; quit;