[Octave-bug-tracker] [bug #51092] mldivide returns wrong matrix size if X contains NaN

[Alois Schlögl]

URL:
  <http://savannah.gnu.org/bugs/?51092>

                 Summary: mldivide returns wrong matrix size if X contains NaN
                 Project: GNU Octave
            Submitted by: schloegl
            Submitted on: Tue 23 May 2017 07:55:51 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.1
        Operating System: GNU/Linux

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Details:

This is example is ok, 


N=1000;D=randn(N,3);C=rand(N,1)>.9;[size(D);size(C);size(D\C);size(mldivide(D,C))]


but when D contains some NaN, the size of the results matrix is wrong. 


N=1000;D=randn(N,3);C=rand(N,1)>.9;D(10,:)=NaN;[size(D);size(C);size(D\C);size(mldivide(D,C))]
warning: matrix singular to machine precision
warning: matrix singular to machine precision
ans =

   1000      3
   1000      1
      3   1000
      3   1000


Although the content might not be meaningful, I would expect that the matrix
size would be the same. I checked also with matlab, and this behaviour is
incompatible with it (matlab returns the correct size). 



In octave, it also seems to make a difference whether the NaN is in the first
column, or only some other column: 


N=1000;D=randn(N,3);C=rand(N,1)>.9;D(10,1)=NaN;[size(D);size(C);size(D\C);size(mldivide(D,C))]
warning: matrix singular to machine precision
warning: matrix singular to machine precision
ans =

   1000      3
   1000      1
      3   1000
      3   1000

N=1000;D=randn(N,3);C=rand(N,1)>.9;D(10,2)=NaN;[size(D);size(C);size(D\C);size(mldivide(D,C))]
 ** On entry to DLASCL parameter number  4 had an illegal value
error: exception encountered in Fortran subroutine dgelsd_
N=1000;D=randn(N,3);C=rand(N,1)>.9;D(10,3)=NaN;[size(D);size(C);size(D\C);size(mldivide(D,C))]
 ** On entry to DLASCL parameter number  4 had an illegal value
error: exception encountered in Fortran subroutine dgelsd_
























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