00100	BEGIN "TEST3"
00200		REQUIRE "ABBREV[SYS,BGB]" SOURCE_FILE;
00300		REQUIRE "DPYIII[SYS,BGB]" SOURCE_FILE;
00400		SAFE INTEGER ARRAY DPYBUF[0:700];
00500		REAL A,B,C,D,M,N,X,Y;
00600		ITG IX,IY,CHR;
00700		STRING S;
00800	
00900	
01000	WHILE TRUE DO
01100	BEGIN "FOREVER"
01200		DPYSET(DPYBUF);
01300		OUTSTR("Y'(+1) = ");S←INCHWL; M ← REALSCAN(S,CHR);
01400		OUTSTR("Y'(-1) = ");S←INCHWL; N ← REALSCAN(S,CHR);
01500		A ← (M+N)/4;
01600		B ← (M-N)/4;
01700		C ← -A;
01800		D ← -B;
     

00100		FOR X ← -1.00 STEP 0.02 UNTIL +1.01 DO
00200	BEGIN
00300		Y ← ((A*X+B)*X+C)*X+D;
00400		IX ← 400*X;
00500		IY ←-511 MAX(250*Y MIN 511);
00600		IF X=-1.00 THEN AIVECT(IX,IY) ELSE AVECT(IX,IY);
00700	END;
00800		AIVECT(-400,-400);
00900		AVECT(+400,-400);
01000		AVECT(+400,+400);
01100		AVECT(-400,+400);
01200		AVECT(-400,-400);
01300		DPYOUT(0);
01400	END "FOREVER";
01500	END "TEST3";