# Category : Files from Magazines

Archive : MATRIX2.ZIP

Filename : MATRIX2.DOC

MATRIX2

MATRIX2 is basically a matrix inversion program to which the

equation solutions have been added. It is configured for up to

32 equations.

Rather than using Gaussian elimination (triangularizing the

input matrix), the program iterates a matrix inversion using

Newton's method. This is desribed in [1].

The significant point is that even though no inverse can be

found for an equation set which includes dependent (or the same)

equations, a solution is found which satisfies the input

equations. (This may be obvious but it surprised me.)

Examples are included on the disk, where they are named mn.dat

where n is an integer. The files mnx.dat have the first equation

repeated, and do not give an invertible matrix. Even so the

program finds a valid solution. Thus if your problem requires

any solution to 3 equations in 4 variables, repeat one of the

three equations, and run the program. I would like to be able to

say something about this solution, but I'm not a mathemetician.

I suspect, based on the few examples herein, that the program

finds the smallest (vector magnitude?) valid solution.

No proof is offerd (or claimed) that the program always finds a

solution which checks. In fact this is clearly impossible for an

input which includes the same equation with different input

solutions, that is parallel lines. In this case the program

apparently finds solutions which solve the independent equations

and averages the input solutions of the parelles lines.

As a check, the output solution vector is plugged back into the

input equations to see if the input solution vector is correctly

computed.

The program monitors a solution error which is the largest

element in the difference matrix I-M*MI where MI is the computed

inverse of M, and I is the identity matrix. For large (over 8)

matrices which apparently invert, this value is typically on the

order of ten to the minus 14 - 16. For small invertible

matrices, it is 0. For matrices mnx.dat which clearly don't

invert, the error is in the range 0.1 - 0.9. The program

includes a warning when the error is greater than 1e-8. This

should caution to continue the iteration, and, if the solution

has converged, recognize that is is not unique.

The program allows input from the keyboard or a disk file. In

the disk file mode it also records the answer. Use the NUL file

to avoid this output.

The program does 20 iterations plus it continues iterating as

long as the error is decreasing. For all but the m32x.dat this

sufficient for convergence. There is a continue option which

allows additional iterations in blocks of 5 plus the tests for

decreasing error. The number of iterations and the solution

error are monitored on the screen.

The program is compiled in Turbo Pascal v5.0. It uses double

precision (8 byte) variables. My machine has an 8087 numerical

processor, however the code for 8087 emulation should be

included; I just don't have any way to try it. With the 8087 the

32 equation matrix takes about 7 minutes on my IBM PC.

I have included the Pascal source code. Any user is welcome to

use and modify the program except for commercial purposes. I

claim all rights to the program, and I disclaim all

responsiblity for the results of using the program whether or

not it gives correct answers. You use the program at your own

risk. I do sincerely thank you for your interest.

William M. Hutchinson

11470 E. Calle Aurora

Tucson, Az. 85748

602-290-8187

[1] 'The Inversion of Large Matrices', Thomas E. Phipps, BYTE

(magazine), April, 1986.

Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/