Lapack: [Version 3.9.0] Infinite loop in slasq3

Created on 21 Jan 2020 · 7Comments · Source: Reference-LAPACK/lapack

When input parameters to "slasq3" follows below pattern:
i0 =3, n0=16, pp=1,desig=0.2f, qmax=0.2f, nfail=4,iter=1, ndiv = 2, ieee = 0, ttype = -1
this function falls into infinite loop in-between code line 332 ~ 362.
100% reproduce.

Source

Peter9606

Most helpful comment

Would you happen to have a complete reproducer for this, in particular with the values contained in the array z ? I cannot reproduce the problem with the data you provided and a random z, ~~and I imagine bad things will happen if~~ not even when any of the array elements is a NaN.

martin-frbg on 1 Feb 2020

👍2

All 7 comments

Do you think this used to work in earlier versions ? AFAIK none of the slasq functions was modified since at least 3.7.0. From your description it is looping as TAU never gets small enough ?

martin-frbg on 26 Jan 2020

Do you think this used to work in earlier versions ? AFAIK none of the slasq functions was modified since at least 3.7.0. From your description it is looping as TAU never gets small enough ?

Sorry, I only verified on 3.9.0 so far for this is the only version at hand.

Peter9606 on 31 Jan 2020

martin-frbg on 1 Feb 2020

👍2

if dmin is nan it should be set to some legit erroneous value; would prevent infinity.

moe123 on 2 Feb 2020

I thought about this as well, but if I am correct about the rules for comparing against NaN this is probably not the problem.

martin-frbg on 2 Feb 2020

No infinite loop using 4b3c7c249f6a2cfed76603d9987cf5164fa6f9e1 to build the code:

      PROGRAM testSLASQ3
      IMPLICIT NONE

*     .. Scalar Arguments ..
      LOGICAL            IEEE
      INTEGER            I0, ITER, N0, NDIV, NFAIL, PP, TTYPE
      REAL               DESIG, DMIN, DMIN1, DMIN2, DN, DN1, DN2, G,
     &                   QMAX, SIGMA, TAU
*     .. Array Arguments ..
      REAL               Z( 64 )
*     .. Subroutines ..
      EXTERNAL           SLASQ3

      PARAMETER ( IEEE=.FALSE. )
      PARAMETER ( I0 = 3 )
      PARAMETER ( QMAX = 1.0 )

      ITER=1
      N0=16
      NDIV=2
      NFAIL=4
      PP=1
      TTYPE=-1
      DESIG=0.2
      DMIN1=0.1
      DMIN2=0.1
      DN=1.0
      DN1=1.0
      DN2=1.0
      G=1.0
      TAU=1.0

      Z = (/0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,
     &      0.1,0.2,0.3,0.4,0.5,0.6,
     &      0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,
     &      0.1,0.2,0.3,0.4,0.5,0.6,
     &      0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,
     &      0.1,0.2,0.3,0.4,0.5,0.6,
     &      0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,
     &      0.1,0.2,0.3,0.4,0.5,0.6/)

      CALL SLASQ3( I0, N0, Z, PP, DMIN, SIGMA, DESIG, QMAX, NFAIL,
     &                   ITER, NDIV, IEEE, TTYPE, DMIN1, DMIN2, DN, DN1,
     &                   DN2, G, TAU )

      END PROGRAM testSLASQ3

weslleyspereira on 22 Apr 2021

👍1

Based on @weslleyspereira post, let us close this issue then.
@Peter9606 thanks for reporting the issue, if the issue comes back, please come back to us.
Julien.