Matrix is close to singular or badly scaled

Hello,

I am receiving the following error when I attempt a simple matrix division within MATLAB. It follows the form of Ax = B. The line of code I have put in to find x is

x = inv(A) * B

It is returning the error:

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 3.938882e-018. > In example at 4

x =

1.0e+019 *

    1.1621
   -0.6298
    7.0903

The values of the A and B matrices are below.

A = [-180 -152 16; -20 -172 -12; -160 20 28]

B = [-13960; -87501; -52408]

I know what the answer for the x matrix should be, but I need the code to make MATLAB do it, and it is miles out. Can anyone help?

[Walter Roberson]

Please consider using the mldivide ('\') operator instead of using inv(); it would be A\B

http://www.mathworks.com/help/techdoc/ref/mldivide.html

Answer 1

[Jan]

A = [-180 -152 16; -20 -172 -12; -160 20 28]
det(A)
% >> 0

A is singular. Then you cannot create the inverse. What do you expect as answer for x then?!

Answer 2

[Richard]

The answer that satisfies all three equations is

x = [50 40 70]

Can you give any indication of how to make this work or improve it? Many thanks.

[Jan]

No. This x does not satisfy the equations:

A = [-180 -152 16; -20 -172 -12; -160 20 28];

B = [-13960; -87501; -52408];

x = [50; 40; 70]; % Column vector!

disp(A * x);

% >> [-13960; -8720; -5240]

A*x is definitely not B.

As I said already: A is singular. Because there is no inverse of a singular matrix, you cannot calculate inv(A)*B. In consequence you can neither make it working nor inmprove it.

Please check the values again for typos.