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PDP-10 Archives
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decuslib10-01
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43,50110/crout1.alg
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100' NAME--CROUT1
110'
120' DESCRIPTION--SOLVES M SETS OF N BY N LINEAR EQUATIONS USING
130' THE CROUT ALGORITHM WITH ROW INTERCHANGES
140'
150' SOURCE--UNKNOWN
160'
170' INSTRUCTIONS--THE DATA TO BE SUPPLIED START IN LINE 1040.
180' THEY ARE THE VALUE OF N, OF M, THE COEFFICIENT MATRIX BY ROWS, AND
190' THE RIGHT HAND SIDE OF THE MATRIX BY COLUMNS.
200' NOTE: IN CASE OF MORE THAN 10 FOR N OR M, THE DIM STATEMENTS IN
210' LINES 260 AND 270 SHOULD BE CHANGES.
220'
230'
240' * * * * * * * MAIN PROGRAM * * * * * * * * * * *
250'
260 DIM A(10, 10)
270 DIM B(10, 10)
280 READ N, M
290 FOR I = 1 TO N
300 FOR J = 1 TO N
310 READ A(I,J)
320 NEXT J
330 NEXT I
340 FOR J = 1 TO M
350 FOR I = 1 TO N
360 READ B(I,J)
370 NEXT I
380 NEXT J
390 REM NOW WE START THE ELIMINATIONS.
400 FOR I = 1 TO N
410 REM HERE WE LOOK FOR THE LARGEST ELEMENT IN A COLUMN.
420 LET X = -1
430 FOR K = I TO N
440 IF ABS( A(K,I) ) <= X THEN 470
450 LET Q = K
460 LET X = ABS( A(K,I) )
470 NEXT K
480 IF X > 0 THEN 510
490 PRINT "MATRIX OF COEFFICIENTS IS SINGULAR....."
500 STOP
510 REM HERE WE START THE INTERCHANGE, IF NEEDED.
520 IF I = Q THEN 630
530 FOR J = 1 TO N
540 LET T = A(I,J)
550 LET A(I,J) = A(Q,J)
560 LET A(Q,J) = T
570 NEXT J
580 FOR J = 1 TO M
590 LET T = B(I,J)
600 LET B(I,J) = B(Q,J)
610 LET B(Q,J) = T
620 NEXT J
630 REM NOW WE ELIMINATE ON THAT ONE ROW.......
640 FOR J = 1 TO N
650 IF I < J THEN 680
660 LET M1 = J - 1
670 GO TO 690
680 LET M1 = I - 1
690 LET S = 0
700 FOR K = 1 TO M1
710 LET S = S + A(I,K) * A(K,J)
720 NEXT K
730 LET A(I,J) = A(I,J) + S
740 IF I >= J THEN 760
750 LET A(I,J) = - A(I,J) / A(I,I)
760 NEXT J
770 NEXT I
780 REM NOW WE HAVE THE REDUCED LEFT HAND SIDE.. NOW STARTS THE RIGHT.
790 FOR J = 1 TO M
800 FOR I = 1 TO N
810 LET S = 0
820 FOR K = 1 TO I-1
830 LET S = S + A(I,K) * B(K,J)
840 NEXT K
850 LET B(I,J) = - ( B(I,J) + S ) / A (I,I)
860 NEXT I
870 FOR I = N TO 1 STEP -1
880 LET S = 0
890 FOR K = I + 1 TO N
900 LET S = S + A(I,K) * B(K,J)
910 NEXT K
920 LET B(I,J) = -B(I,J) + S
930 NEXT I
940 NEXT J
950 REM NOW WE START THE PRINTOUT.....
960 FOR J = 1 TO M
970 PRINT
980 PRINT "ANSWER SET ";J
990 FOR I = 1 TO N
1000 PRINT B(I,J),
1010 NEXT I
1020 NEXT J
1030 STOP
1040 DATA
1100 END