Jsun Yui Wong

"Solving systems of nonlinear equations is perhaps the most difficult problem in all of numerical computations," Rice [7, 1993, p. 355].

"We make an extreme, but wholly defensible, statement: There are *no* good, general methods for solving systems of more than one nonlinear equation. Furthermore, it is not hard to see why (very likely) there *never will be* any good, general methods," Press, Teukolsky, Vetterling, and Flannery [6, 2007, p. 473].

"Solving a system of nonlinear equations is a problem that is avoided where possible, customarily by approximating the nonlinear system by a system of linear equations. When this is unsatisfactory, the problem must be tackled directly," Burden, Faires, and Burden [1, 2016, page 642].

Using qb64v1000-win [8], the following computer program seeks to solve simultaneously Brown's almost linear system of 30000 equations; see Morgan [5, page 15], Floudas [2, page 660], and Han and Han [3, page 227, Example 3]. While line 128 of the preceding paper is 128 FOR I = 1 TO 6000000 STEP 1, here line 128 is 128 FOR I = 1 TO 15000000 STEP 1.

0 DEFDBL A-Z

3 DEFINT J, K

4 DIM X(30003), A(30003), L(30003), K(30003)

5 FOR JJJJ = -32000 TO 32000

14 RANDOMIZE JJJJ

16 M = -1D+50

91 FOR KK = 1 TO 30000

94 A(KK) = RND * 2.75

95 NEXT KK

128 FOR I = 1 TO 15000000 STEP 1

129 FOR K = 1 TO 30000

131 X(K) = A(K)

132 NEXT K

155 FOR IPP = 1 TO FIX(1 + RND * 3)

181 B = 1 + FIX(RND * 30000)

183 R = (1 - RND * 2) * A(B)

187 IF RND < .25 THEN X(B) = A(B) + RND * R ELSE IF RND < .333 THEN X(B) = A(B) + RND ^ 4 * R ELSE IF RND < .5 THEN X(B) = A(B) + RND ^ 7 * R ELSE X(B) = CINT(A(B))

191 NEXT IPP

301 prodd = 1

305 FOR j55 = 2 TO 30000

311 prodd = prodd * X(j55)

321 NEXT j55

371 IF prodd < .00001 THEN 1670

389 X(1) = (1) / prodd

501 summ = 0

505 FOR j27 = 1 TO 30000

511 summ = summ + X(j27)

521 NEXT j27

901 DIFF = 0

905 FOR J77 = 1 TO 29999

911 DIFF = DIFF - ABS(X(J77) + summ - 30001)

921 NEXT J77

995 P = DIFF

1451 IF P <= M THEN 1670

1657 FOR KEW = 1 TO 30000

1658 A(KEW) = X(KEW)

1659 NEXT KEW

1661 M = P

1670 NEXT I

1890 REM IF M < -.0005 THEN 1999

1912 PRINT A(1), A(2), A(3)

1915 PRINT A(4), A(5), A(6)

1917 PRINT A(7), A(8), A(9)

1919 PRINT A(10), A(11), A(12)

1928 PRINT A(29988), A(29989), A(29990)

1930 PRINT A(29991), A(29992), A(29993)

1931 PRINT A(29994), A(29995), A(29996)

1933 PRINT A(29997), A(29998), A(29999)

1939 PRINT A(30000), M, JJJJ

1999 NEXT JJJJ

This computer program was run with qb64v1000-win [8]. Copied by hand from the screen, the computer program’s complete output through

JJJJ= -32000 is shown below.

1.000000264189365 .99999999999928 1

1 1 1

1 1 1

1 1 1.000000010180462

1 1 1

1 1 1

1.000000041739135 1 1

1.00000000000503 .9999999997940903 1

1.000000393541283 -3.665219392019026D-03 -32000

Above there is no rounding by hand; it is just straight copying by hand from the screen.

One notes that of the 30000 values for the 30000 unknowns, only the 25 A's of line 1912 through line 1939 of the computer program above are shown above and that the M of line 1939 is essentially defined in line 911, line 995, and line 1661, which are 911 DIFF = DIFF - ABS(X(J77) + summ - 30001), 995 P = DIFF, and 1661 M = P, respectively. This M includes 29999 absolutes values.

On a personal computer with a Pentium Dual-Core CPU E5200 @2.50GHz, 2.50 GHz, 960 MB of RAM and with qb64v1000-win [8], the wall-clock time for obtaining the output through JJJJ= -32000 was twelve hours.

**Acknowledgment**

I would like to acknowledge the encouragement of Roberta Clark and Tom Clark.

References

[1] R. L. Burden, J. D. Faires, Annette M. Burden. *Numerical Analysis, Tenth Edition*. Cengage Learning, 2016.

[2] C. A. Floudas, *Deterministic Global Optimization*. Kluwer Academic Publishers, 2000.

[3] Tianmin Han, Yuhuan Han, Solving Large Scale Nonlinear Equations by a New ODE Numerical Integration Method, *Applied Mathematics*, 2010, 1, 222-229.

http://www.SciRP.org/journal/am

[4] Microsoft Corp. *BASIC, second edition* (May 1982), Version 1.10. Boca Raton, Florida: IBM Corp., Personal Computer, P. O. Box 1328-C, Boca Raton, Florida 33432, 1981.

[5] Alexander P. Morgan, A Method for Computing All Solutions to Systems of Polynomial Equations, *ACM Transactions on Mathematical Software*, Vol. 9, No. 1, March 1983, Pages 1-17. https://folk.uib.no/ssu029/pdf_file/Morgan83.pdf

[6] W. H. Press, S. A. Teukolsky, W. T. Vetterling, B. P. Flannery. *Numerical recipes: the art of* *scientific computing, third ed*. Cambridge University Press, 2007.

[7] J. Rice. *Numerical Methods, Software, and Analysis, Second Edition*. Academic Press, 1993.

[8] Wikipedia, QB64, https://en.wikipedia.org/wiki/QB64

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