[Octave-bug-tracker] [bug #56232] Octave crash when inverting an empty sparse matrix.

[Marco Caliari]

Follow-up Comment #19, bug #56232 (project octave):

octave 5.1.1


warning: lu: function may fail when called with less than 4 output arguments
and a sparse input
UMFPACK V5.7.6 (May 4, 2016), Control:
    Matrix entry defined as: double
    Int (generic integer) defined as: SuiteSparse_long

    0: print level: 6
    1: dense row parameter:    0.2
        "dense" rows have    > max (16, (0.2)*16*sqrt(n_col) entries)
    2: dense column parameter: 0.2
        "dense" columns have > max (16, (0.2)*16*sqrt(n_row) entries)
    3: pivot tolerance: 0.1
    4: block size for dense matrix kernels: 32
    5: strategy: 0 (auto)
    10: ordering: 1 AMD/COLAMD
    11: singleton filter: enabled
    6: initial allocation ratio: 0.7
    7: max iterative refinement steps: 2
    13: Q fixed during numerical factorization: 1 (yes)
    14: AMD dense row/col parameter:    10
       "dense" rows/columns have > max (16, (10)*sqrt(n)) entries
        Only used if the AMD ordering is used.
    15: diagonal pivot tolerance: 0.001
        Only used if diagonal pivoting is attempted.
    16: scaling: 0 (no)
    17: frontal matrix allocation ratio: 0.5
    18: drop tolerance: 0
    19: AMD and COLAMD aggressive absorption: 1 (yes)

    The following options can only be changed at compile-time:
    8: BLAS library used:  Fortran BLAS.  size of BLAS integer: 4
    compiled for ANSI C
    POSIX C clock_getttime.
    computer/operating system: Linux
    size of int: 4 SuiteSparse_long: 8 Int: 8 pointer: 8 double: 8 Entry: 8
(in bytes)

column-form matrix, n_row 2 n_col 2, nz = 0. ERROR: Ai missing


UMFPACK:  Copyright (c) 2005-2013 by Timothy A. Davis.  All Rights Reserved.


UMFPACK License:  refer to UMFPACK/Doc/License.txt for the license.
   UMFPACK is available under alternate licenses,
   contact T. Davis for details.


Availability: http://www.suitesparse.com
UMFPACK V5.7.6 (May 4, 2016): ERROR: required argument(s) missing

UMFPACK V5.7.6 (May 4, 2016), Info:
    matrix entry defined as:          double
    Int (generic integer) defined as: SuiteSparse_long
    BLAS library used: Fortran BLAS.  size of BLAS integer: 4
    MATLAB:                           no.
    CPU timer:                        POSIX C clock_getttime ( ) routine.
    number of rows in matrix A:       2
    number of columns in matrix A:    2
    memory usage reported in:         16-byte Units
    size of int:                      4 bytes
    size of SuiteSparse_long:         8 bytes
    size of pointer:                  8 bytes
    size of numerical entry:          8 bytes

    strategy used:                    unsymmetric
    ordering used:                    not computed
    symbolic factorization defragmentations:       0

    symbolic/numeric factorization:      upper bound               actual     
%
    variable-sized part of Numeric object:

error: lu: sparse_lu: symbolic factorization failed


matlab 9.6.0.1099231 (R2019a) Update 1

pivot threshold: 1
sprealloc in lu(L): 2 1 1 3
Pruned nzs: 2
L nonzeros: 2
U nonzeros: 0

ans =

   All zero sparse: 2×2


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