Re: Singular matrix

[c.]

On 3 Oct 2016, at 15:39, Bernardo Sulzbach <address@hidden> wrote:

> The warning you mentioned happens again after A changes. As repeating a 
> command is not so common (or useful), I think it is fine the way it is.

This happens because before you run A \ b the properties of A are unknown:

>> A = [1 2; 1 2]; b = [1; 1];
>> matrix_type (A)
ans = Full

but when you invoke A \ b Octave tries a factorization and 
discovers A is singular and issues the warning

>> A \ b
warning: matrix singular to machine precision
ans =

   0.20000
   0.40000

and it also marks A as singular so it does not need to check again

>> matrix_type (A)
ans = Singular

So next time you try there is no warning

>> A \ b
ans =

   0.20000
   0.40000


c.