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IDProjectCategoryView StatusDate SubmittedLast Update
0007903ITKpublic2008-10-30 20:382008-12-17 23:01
ReporterHans Johnson 
Assigned To 
PriorityhighSeverityminorReproducibilityalways
StatusclosedResolutionfixed 
PlatformOSOS Version
Product VersionITK-3-8 
Target VersionFixed in VersionITK-3-10 
Summary0007903: Bug in vnl_powell.cxx
DescriptionHello VXL Developers,

I was producing inconsistent results in my medical image processing software when using powell optimization in my code that prompted me to run valgrind (See report at end of this message).

The least invasive way to avoid this bug is to initialize the variable “bx=0” on lines 87 and 124. This, however, is not the best solution in my opinion. Currently the the powell optimizer uses vn_brent.h which states in it’s header
==============================
//: Brent 1D minimizer (deprecated)
//
// Please use vnl_brent_minimizer instead.
//
// This routine used to contain copyrighted code, and is deprecated.
// It is now simply a wrapper around vnl_brent_minimizer.
==============================

I’ve made a minimally modified version of vnl_powell.cxx that uses vnl_brent_minimizer directly (saving 3 levels of indirect function calls) that makes it much easier to read and removes the errors.

http://www.nitrc.org/plugins/scmsvn/viewcvs.php/trunk/lib/vnl_powell_fixed.cxx?revision=172&root=art&sortdir=down&view=markup [^]

In my program, this fix reliably runs to completion in 24 seconds where it had been occasionally segmentation faulting or running somewhere between 120 seconds to 300 seconds depending on what value was being filled in.

Please consider implementing this bug fix in the next release of vxl.

Thanks,
Hans J. Johnson
hans-johnson@uiowa.edu

## Valgrind is our friend!

  ==15048== Conditional jump or move depends on uninitialised value(s)
  ==15048== at 0x890BE9: vnl_bracket_minimum(vnl_cost_function&, double&, double&, double&, double&, double&, double&) (vnl_bracket_minimum.cxx:46)
  ==15048== by 0x890938: vnl_brent::bracket_minimum(double*, double*, double*, double*, double*, double*) (vnl_brent.cxx:58)
  ==15048== by 0x8908E0: vnl_brent::bracket_minimum(double*, double*, double*) (vnl_brent.cxx:52)
  ==15048== by 0x88F876: vnl_powell::minimize(vnl_vector<double>&) (vnl_powell.cxx:85)
  ==15048== by 0x676E4D: PowellOptimizeMSP(itk::SmartPointer<itk::OrientedImage<short, 3> >&, itk::Point<double, 3> const&, itk::Point<double, 3> const&, itk::Point<double, 3> const&, PlaneObject const&, itk::Point<double, 3>&, Plan
eObject&, double) (acpcdetect_itk.cxx:361)
  ==15048== by 0x678079: ComputeMSP(itk::SmartPointer<itk::OrientedImage<short, 3> >, PlaneObject&, itk::Point<double, 3>&, itk::Matrix<double, 3, 3>&, unsigned) (acpcdetect_itk.cxx:679)
  ==15048== by 0x678571: computeTmsp(itk::SmartPointer<itk::OrientedImage<short, 3> >&, PlaneObject&, itk::Point<double, 3>&) (acpcdetect_itk.cxx:739)
  ==15048== by 0x56D4C8: main (acpcResampleMSP.cxx:74)



vnl_powell.cxx
====================
lines 82-85 && lines 122-125
       double ax = 0.0;
       double xx = initial_step_;
       double bx; /**NOTE bx is not initialized!*/
       brent.bracket_minimum(&ax, &xx, &bx);

vnl_brent.cxx
====================
lines 49-59
 void vnl_brent::bracket_minimum(double *ax, double *bx, double *cx) //**NOTE cx is not initialized
 {
   double fa, fb, fc;
   bracket_minimum(ax,bx,cx,&fa,&fb,&fc);
 }

 void vnl_brent::bracket_minimum(double *ax, double *bx, double *cx, //**NOTE cx is not initialized
                                 double *fa, double *fb, double *fc)
 {
   vnl_bracket_minimum( *f_, *cx, *bx, *ax, *fc, *fb, *fa );
                            /*^----------- NOTE: cx is not initialized */
 }

vnl_bracket_minimum.cxx
====================
lines 38-48

 void vnl_bracket_minimum(vnl_cost_function& fn,
                         double& a, double& b, double& c, //** Note a is not initialized
                         double& fa, double& fb, double& fc)
 {
   // Set up object to evaluate function
   // Note that fn takes a vector input - f converts a scalar to a vector
   vnl_bm_func f(fn);

   if (b==a) b=a+1.0;
        /*^-------------- Note comparison of value where a is not initialized. In my case, a=324e+124 sometimes
   fa = f(a);
        /*^-------A not initialized here, and should not be used (this is bx in the original calling function.*/
   fb = f(b);


TagsNo tags attached.
Resolution Date
Sprint
Sprint Status
Attached Filescxx file icon vnl_powell_fixed.cxx [^] (4,379 bytes) 2008-10-30 20:38
? file icon vnl_powell_fixed.h [^] (1,459 bytes) 2008-10-30 20:39

 Relationships

  Notes
(0014004)
Luis Ibanez (manager)
2008-10-31 17:27

Committed the fix after running an Experimental build on Zion.

http://public.kitware.com/cgi-bin/viewcvs.cgi/Utilities/vxl/core/vnl/algo/vnl_powell.cxx?root=Insight&r1=1.4&r2=1.5&sortby=date [^]
(0014388)
Hans Johnson (developer)
2008-12-17 23:00

The bug fix was also propogated to vxl repository.
(0014389)
Hans Johnson (developer)
2008-12-17 23:01

Tested and confirmed to work now. This fix was also propogated to the vxl source tree.

 Issue History
Date Modified Username Field Change
2008-10-30 20:38 Hans Johnson New Issue
2008-10-30 20:38 Hans Johnson File Added: vnl_powell_fixed.cxx
2008-10-30 20:39 Hans Johnson File Added: vnl_powell_fixed.h
2008-10-31 17:27 Luis Ibanez Note Added: 0014004
2008-12-17 23:00 Hans Johnson Note Added: 0014388
2008-12-17 23:01 Hans Johnson Note Added: 0014389
2008-12-17 23:01 Hans Johnson Status new => closed
2008-12-17 23:01 Hans Johnson Resolution open => fixed
2008-12-17 23:01 Hans Johnson Fixed in Version => ITK-3-10


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