[bug #58763] gsl_root_fsolver_bren produces wrong results when run under valgrind

[Sergei Ossokine]

URL:
  <https://savannah.gnu.org/bugs/?58763>

                 Summary:  gsl_root_fsolver_bren produces wrong results when
run under valgrind
                 Project: GNU Scientific Library
            Submitted by: sergei1387
            Submitted on: Tue 14 Jul 2020 09:25:00 AM UTC
                Category: Runtime error
                Severity: 3 - Normal
        Operating System: 
                  Status: None
             Assigned to: None
             Open/Closed: Open
                 Release: 2.5
         Discussion Lock: Any

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Details:

When running with valgrind to check for memory leaks, the solver incorrectly
sets x_lower and x_upper which results in it exiting immediately without
finding a root. This happens even with the basic demo program for 1D
root-finding. This does not happen for the other 2 types of solvers, namely
gsl_root_fsolver_bisection and gsl_root_fsolver_falsepos. 

Here is the example of the expected program output (no valgrind):


$ ./demo 
using brent method
 iter [    lower,     upper]      root        err  err(est)
    1 [1.0000000, 5.0000000] 1.0000000 -1.2360680 4.0000000
    2 [1.0000000, 3.0000000] 3.0000000 +0.7639320 2.0000000
    3 [2.0000000, 3.0000000] 2.0000000 -0.2360680 1.0000000
    4 [2.2000000, 3.0000000] 2.2000000 -0.0360680 0.8000000
    5 [2.2000000, 2.2366300] 2.2366300 +0.0005621 0.0366300
Converged:
    6 [2.2360634, 2.2366300] 2.2360634 -0.0000046 0.0005666


And here is running with valgrind:

valgrind ./demo 
==14950== Memcheck, a memory error detector
==14950== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==14950== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==14950== Command: ./demo
==14950== 
using brent method
 iter [    lower,     upper]      root        err  err(est)
Converged:
    1 [5.0000000, 5.0000000] 5.0000000 +2.7639320 0.0000000
==14950== 
==14950== HEAP SUMMARY:
==14950==     in use at exit: 0 bytes in 0 blocks
==14950==   total heap usage: 2 allocs, 2 frees, 112 bytes allocated
==14950== 
==14950== All heap blocks were freed -- no leaks are possible
==14950== 
==14950== For counts of detected and suppressed errors, rerun with: -v
==14950== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)



The code was compiled with


gcc -g -Wall -O2 demo.c -o demo -lgsl -lgslcblas -lm


using gcc version 10.1.0



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File Attachments:


-------------------------------------------------------
Date: Tue 14 Jul 2020 09:25:00 AM UTC  Name: demo.c  Size: 1KiB   By:
sergei1387
demo.c is the main file demo_fn.* define the quadratic function being used for
root finding
<http://savannah.gnu.org/bugs/download.php?file_id=49481>
-------------------------------------------------------
Date: Tue 14 Jul 2020 09:25:00 AM UTC  Name: demo_fn.c  Size: 666B   By:
sergei1387
demo.c is the main file demo_fn.* define the quadratic function being used for
root finding
<http://savannah.gnu.org/bugs/download.php?file_id=49482>
-------------------------------------------------------
Date: Tue 14 Jul 2020 09:25:00 AM UTC  Name: demo_fn.h  Size: 228B   By:
sergei1387
demo.c is the main file demo_fn.* define the quadratic function being used for
root finding
<http://savannah.gnu.org/bugs/download.php?file_id=49483>

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