100 '- SOLV.BAS-A program to solve equations in one unknown -
110 KEY OFF : SCREEN 0: COLOR 14, 1 : CLS: DEFINT I-N
120 LOCATE 2, 20: PRINT "- SOLV - SOLVER OF EQUATIONS IN ONE UNKNOWN -":PRINT
130 PRINT SPC(12);"by Max Chandivert - MS/PC-DOS Interpreter version - 900822"
140 A$ ="6*X^5 -13*X^4 +27*X*X*X +7*X*X -29*X +10"
150 PRINT: PRINT "F(X) = "A$
160 PRINT "Is another expression required Y/N? : .: R$ = INPUT$(1)
170 PRINT R$: IF R$ = "N" OR R$ = "n" THEN 220
180 INPUT "New expression in BASIC code: F(X) _ ",A$
190 F$ = "TTT.BAS": OPEN F$ FOR OUTPUT AS #1
200 PRINT #1, "140 A$ ="+CHR$(34)+A$+CHR$(34): CLOSE #1
210 CHAIN MERGE F$, 140
220 F$ = "TTT.BAS"
230 OPEN F$ FOR OUTPUT AS #1: PRINT #l, "250 DEF FNF(X)="+A$: CLOSE #1
240 CHAIN MERGE F$, 250
250 DEF FNF(X)=6*X^5 -13*X^4 +27*X*X*X +7*X*X -29*X +10
260 TOL1=.000001: TOL2=1!: PRINT: PRINT "TOL1, TOL2: ";TOL1,TOL2
270 PRINT "Do you wish to change those values, Y/N? : ,: R$ = INPUT$(1)
280 PRINT R$
290 IF R$ _ "Y" OR R$ = "y" THEN INPUT "Enter new values: ",TOL1, TOL2
300 PRINT: INPUT "Enter A,B trial values for X: ",A,B
310 IF A<B THEN TEMP=A: A=B: B=TEMP
320 YA = FNF(A): YB = FNF(B): ITAG = 0
330 PRINT :PRINT "Initial values of Y are YA,YB= "YA, YB
340 IF ABS(YA) < TOLl THEN G = A: N = 0: GOTO 540
350 IF ABS(YB) < TOLI THEN G = B: N = 0: GOTO 540
360 PRINT : PRINT "Successive trial values of variable, and resulting Y."
370 FOR N=1 TO 50
380 I=SGN(YA)*SGN(YB): SLOPE = (YB-YA)/(B-A): G = B-YB/SLOPE
390 YG = FNF(G) ': PRINT N, I, ITAG To facilitate development
400 IF ABS(YG) < TOLl THEN 540
410 IF ABS(YG) < ABS(YB) THEN 510
420 IF I=1 THEN ITAG=ITAG+l ELSE ITAG=0: GOTO 510 'YA, YB are opposite signs
430 IF ITAG > 2 THEN 450 ' Now YA, YB have same sign
440 IF ABS(SLOPE)<TOL2 THEN G = B - YB/TOL2: GOTO 490 ELSE GOTO 510
450 YAA = FNF(A+.001*ABS(A)): YBB = FNF(B+.001*ABS(B))
460 IF YAA>YA THEN IDA =1 ELSE IDA --1
470 IF YBB>YB THEN IDB -1 ELSE IDB --1
480 IF IDA*IDB = -1 THEN G = .5*(A+B) ELSE 510
490 YG = FNF(G)
500 IF ABS(YG)<TOLl THEN 540
510 A=B: B=G: YA=YB: YB=YG
520 PRINT G, YG: NEXT
530 PRINT "N= "N"-NO SOLUTION FOUND": GOTO 560
540 PRINT "Y within ";TOL1:" of ZERO for X= ";G
550 PRINT "There was ";N;" iteration(s)."
560 PRINT: PRINT "Try other starting values A, B, Y/N? : ";: R$ =  INPUT$(1)
570 PRINT R$: IF R$ = "Y" OR R$ = "y" THEN 300
580 PRINT "Solve another equation, Y/N? : " ;: R$ = INPUT'$(1): PRINT R$
590 IF R$ = "Y" OR R$ = "y" THEN CLS: GOTO "183 ELSE KILL "TTT.BAS": END