[Octave-bug-tracker] [bug #58398] Given an integer matrix, the characteristic polynomial has none integer value

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?58398>

                 Summary: Given an integer matrix, the characteristic
polynomial has none integer value
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Tue 19 May 2020 02:12:20 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: muslim
        Originator Email: address@hidden
             Open/Closed: Open
                 Release: 5.2.0
         Discussion Lock: Any
        Operating System: GNU/Linux

    _______________________________________________________

Details:

I have a recursive function for constructing a special NxN integer matrix
which contains only 0,1, or -1. (N is even)

function C=getC(N)
  if N==2
    C=[0,1;-1,-1];
  else
    Y=zeros(N,N);
    Y(1,N)=-1;
    Y(N,2)=-1;
    Y(N/2, 1)=-1;
    Y(2:N-1,2:N-1)=getC(N-2);
    C=Y;
end

But when N>=50, poly(getC(N)) will have non integer values.
When N>= 70 , roots(poly(getC(N))) will not equal to eig(getC(N)).

I have tried some other random matrices, but all of them are correct, which
means roots(poly(A)) = eig(A). It seems only my matrix will bring this error.



    _______________________________________________________

File Attachments:


-------------------------------------------------------
Date: Tue 19 May 2020 02:12:20 AM UTC  Name: main_getC.m  Size: 176B   By:
None

<http://savannah.gnu.org/bugs/download.php?file_id=49118>
-------------------------------------------------------
Date: Tue 19 May 2020 02:12:20 AM UTC  Name: getC.m  Size: 164B   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=49119>

    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?58398>

_______________________________________________
  Message sent via Savannah
  https://savannah.gnu.org/