1000 REM ***** MODIFIED TO RUN ON PDP-11-20 *****
1100 REM ***** PHIL ZUMSTEG ***** 4/20/72
8900 DEF FNF(Y)=-X/Y
9000 REM***** DEQFO ***** MATHEMATICS PROGRAM *****
9001 REM***** VERSION 1 ***** 7/31/69 *****
9002 REM SOLVES A FIRST ORDER DIFFERENTIAL EQUATION
9003 REM DEF FNF(Y)= ??
9004 READ X0,Y,H,L,B
9005  X=X0
9006 E=1/L
9007 IF (B-X0)*H>0 THEN9009
9008 H=-H
9009 IF (B-X0)*L>0 THEN 9011
9010 L=-L
9011 PRINT "VALUE OF X","VALUE OF Y"
9012 PRINT
9013 PRINT X,Y
9014 GO TO 9018
9015 P=Y+H*FNF(Y)
9016 X=X+H
9017 Y=(Y+P)/2+H/2*FNF(P)
9018 IF (X+H-B)*SGN(L)+1.E-07>=0 THEN 9021
9019 R=X+H
9020 GO TO 9022
9021 R=B
9022 A=INT(E*R)/E+L*(SGN(H)-1)/2
9023 IF (A+L-R)*SGN(L)-1.E-07>=0 THEN 9025
9024 A=A+L
9025 IF (X-A)*SGN(L)+1.E-07>=0 THEN 9028
9026 Q=A
9027 GO SUB 9034
9028 IF R=B THEN 9030
9029 GO TO 9015
9030 IF ABS(R-A)<.5*.000001 THEN 9033
9031 Q=R
9032 GO SUB 9034
9033 GO TO 9999
9034 P1=Y+(Q-X)*FNF(Y)
9035 X1=X
9036 X=Q
9037 Y1=(Y+P1)/2+(Q-X1)/2*FNF(P1)
9038 X=X1
9039 PRINT Q,Y1
9040 RETURN
9900 DATA 0,1,.01,.1,1
9999 END