# suspicious bug report

• Subject: suspicious bug report
• From: "itleou" <itleou@et4.thit.edu.tw>
• Date: Mon, 12 Apr 2004 01:37:00 +0800
• Content-Type: text/plain; charset=big5

Hello :
I input the following two matrices with different precision. And try to
find the invers matrices.

Matirx 1

-0.007813040763535813	0.09404650596542488	0.007137350465219316
0.043771682120831414	0.0030207767015258628	0.0017426788812630084
-0.08840246837497706	0.1658191105607822	-2.1684043449710089E-19

The inverse is.
27811547190376133000.00000000 2660470675396094500.00000000
-4611686018427386900.00000000
2660470675396094500.00000000 254502353507749056.00000000
-441156881067223490.00000000
-4611686018427387900.00000000 -441156881067223550.00000000
764705673761224450.00000000

This inverse matirx is wrong.

After I trimed the precison of the matrix up to 8th decimal. I got matrix 2.
Matrix 2.
0.00069069 -0.00781304 -0.00034199
-0.00781304  0.09404651  0.00713735
-0.00034199  0.00713735  0.00205509
And I got the correct inverse matrix.
-514148121.34733210 -49183743.09743571 85255668.98622870
-49183743.09743572 -4704934.35844128 8155562.50155896
85255668.98622869 8155562.50155896 -14136372.51113162

This computation reveals that there is something wrong in the construtor.
So I print out LU array at the end of the constructor for matrix 1.
At the end of LUDecomposition constructor LU=
-0.007813040763535813	0.09404650596542488	0.007137350465219316
0.043771682120831414	0.0030207767015258628	0.0017426788812630084
-0.08840246837497706	0.1658191105607822	-2.1684043449710089E-19

Also the LU array at the end of the constructor for matrix 2.
in the end of LUDecomposition constructor LU=
-0.00781304	0.09404651	0.00713735
0.043771694500476126	0.0030207748954440266	0.0017426760962570265
-0.08840220963926973	0.16581152525370552	1.1729425290903876E-8

NOTICE: The elements at (3,3) are different.

itleou@et4.thit.edu.tw
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