wrong calculation of inverse matrix

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bencsl
bencsl on 7 Apr 2019
Commented: Torsten on 8 Apr 2019
i have got a matrix
a=[ 8.371925000000001 -2.352900000000000 -4.033370000000001 1.019405000000000 -0.588200000000000;
-2.352900000000000 4.876890000000000 0 -0.588200000000000 1.044959999999999;
-4.033337000000000 0 4.033337000000000 0.000000000000000 0;
-1.064795000000001 0.588200000000000 0 8.113875000000000 8.113875000000000;
0.588200000000000 -1.093040000000000 0 -2.352900000000000 -2.352900000000000]
inv(a)
which give out
0.355615858390428 0.350051331178662 0.355618767972078 0.250754989305270 0.931280985155553
0.107719602768672 0.106034051782392 0.107720484110075 -0.238400306760741 -0.801950621197803
0.355615858390428 0.350051331178662 0.603552426875364 0.250754989305270 0.931280985155553
-0.165804799871048 -0.775520233961580 -0.165806156454541 -0.962196522948301 -3.621064878674608
0.204663830554452 0.813771214895349 0.204665505075180 1.135631499365114 3.801414057331816
and the ans is wrong, did i get any thing wrong?
螢幕快照 2019-04-08 上午2.12.14.png
  4 Comments
David Goodmanson
David Goodmanson on 7 Apr 2019
Hi bencsl,
for what reason are you thinking that the answer is wrong? I tried b = inv(a) and got your Matlab result. Then checking a*b vs the identity matrix,
max(max(abs(b*a-eye(5))))
ans = 3.5527e-15 % should be small
so if any inverse is incorrect, it's the one in the image.
Torsten
Torsten on 8 Apr 2019
Maybe you have to consider more digits for the entries in matrix a to get the result in the image.

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