[Octave-bug-tracker] [bug #62867] wrong result when solving large-scale linear equation

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?62867>

                 Summary: wrong result when solving large-scale linear
equation
                 Project: GNU Octave
               Submitter: None
               Submitted: Fri 05 Aug 2022 07:48:14 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: Junjie Yu
        Originator Email: junjieyu@usc.edu
             Open/Closed: Open
                 Release: 7.2.0
         Discussion Lock: Any
        Operating System: Any


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Follow-up Comments:


-------------------------------------------------------
Date: Fri 05 Aug 2022 07:48:14 PM UTC By: Anonymous
I was working on running some Matlab files in Octave (7.2.0) and got an
incorrect answer. After digging for a while, I found Octave meets 'matrix
singular to machine precision' warning when solving large-size linear
equations. Below I provide a simple test case for reproducing the error.
We want to solve a linear system: A*x = rhs(see test.m file)
Where A has dimension 93248*93248 and is very sparse, rhs has the dimension of
93248*1.
we can solve x using x = mldivide(A, rhs);
matlab can solve this correctly, octave lead to precision error and give a
totally wrong result.


octave-output:
warning: matrix singular to machine precision, rcond = 1.31465e-17
warning: called from
    test at line 6 column 3

ans = -0.027239

matlab-output:
ans =

   6.7878e+11

Could you check whether you can reproduce this error and give me any
suggestions to handle this?
Thanks so much!










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