[Octave-bug-tracker] [bug #35243] Error with y=x^(1/3)

[Kurt Strein]

URL:
  <http://savannah.gnu.org/bugs/?35243>

                 Summary: Error with y=x^(1/3)
                 Project: GNU Octave
            Submitted by: kurt_strein
            Submitted on: Thu 05 Jan 2012 04:31:59 AM GMT
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.2.4
        Operating System: Microsoft Windows

    _______________________________________________________

Details:

Bug report for Octave 3.2.4 configured for i686-pc-mingw32

Description:
-----------

  * Error with y=x^(1/3)
Type in the following:
octave-3.2.4.exe:2> x=-1.7987e8
x= -179870000
octave-3.2.4.exe:3> y=x^(1/3)
y= 282.24 + 488.86i
octave-3.2.4.exe:4> w=y*y*y
w=-1.7987e+008 + 5.9605e-008i
Thus the provided answer is one of the two imaginary number answers and not
the one real number answer.
What the answer should be is
x=-1.7987e8
y= x^(1/3)=-564.4809

A second test with x=-27
octave-3.2.4.exe:2> x=-27
x= -27
octave-3.2.4.exe:3> y=x^(1/3)
y= 1.5000 + 2.5981i
octave-3.2.4.exe:4> w=y*y*y
w=-2.7000e+001 + 3.5527e-015i
So it once again gave one of the imaginary answers and not the one real answer
of -3.0
Repeat-By:
---------

  * Please replace this item with a description of the sequence of
    events that causes the problem to occur. 

Fix:
---

  * If possible, replace this item with a description of how to
    fix the problem (if you don't have a fix for the problem, don't
    include this section, but please do submit your report anyway).



Configuration (please do not edit this section):
-----------------------------------------------

uname output:     Windows
configure opts:   
Fortran compiler: mingw32-gfortran-4.4.0-dw2
FFLAGS:           -O -mieee-fp
FLIBS:            -lgfortran
CPPFLAGS:         -I/usr/local/octmgw32_gcc-4.4.0-dw2/include
INCFLAGS:         -I. -I/octmgw32/octave/octave-3.2.4 -I. -I./liboctave
-I./src -I./libcruft/misc -I/octmgw32/octave/octave-3.2.4
-I/octmgw32/octave/octave-3.2.4/liboctave -I/octmgw32/octave/octave-3.2.4/src
-I/octmgw32/octave/octave-3.2.4/libcruft/misc
C compiler:       mingw32-gcc-4.4.0-dw2, version4.4.0 (GCC) 
CFLAGS:           -march=i686 -mtune=generic -O3 -Wall
CPICFLAG:         
C++ compiler:     mingw32-g++-4.4.0-dw2, version4.4.0
CXXFLAGS:         -D_GLIBCXX_DLL -march=i686 -mtune=generic -O3 -Wall
CXXPICFLAG:       
LD_CXX:           mingw32-g++-4.4.0-dw2
LDFLAGS:          -shared-libgcc -Wl,--allow-multiple-definition
LIBFLAGS:         -L.
RLD_FLAG:         
BLAS_LIBS:        -llapack -lblas
FFTW_LIBS:        -lfftw3 -lfftw3f
LIBS:             -lreadline  -lncurses -liberty -lhdf5 -lz -lm  -lgdi32
-lws2_32 -luser32 -lkernel32
LEXLIB:           
LIBGLOB:          -lglob
SED:              /usr/bin/sed
DEFS:
-DPACKAGE_NAME="" -DPACKAGE_TARNAME="" -DPACKAGE_VERSION=""
-DPACKAGE_STRING="" -DPACKAGE_BUGREPORT="" -DOCTAVE_SOURCE=1 -DSTDC_HEADERS=1
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-DHAVE_MEMORY_H=1 -DHAVE_STRINGS_H=1 -DHAVE_INTTYPES_H=1 -DHAVE_STDINT_H=1
-DHAVE_UNISTD_H=1 -D__EXTENSIONS__=1 -D_ALL_SOURCE=1 -D_GNU_SOURCE=1
-D_POSIX_PTHREAD_SEMANTICS=1 -D_TANDEM_SOURCE=1 -DSEPCHAR=';'
-DSEPCHAR_STR=";" -D__NO_MATH_INLINES=1 -DCXX_NEW_FRIEND_TEMPLATE_DECL=1
-DCXX_ISO_COMPLIANT_LIBRARY=1 -DHAVE_PTHREAD=1 -DHAVE_X_WINDOWS=1
-DHAVE_LIBM=1 -DHAVE_QHULL=1 -DHAVE_PCRE_COMPILE=1 -DHAVE_PCRE=1
-DHAVE_REGEX=1 -DHAVE_ZLIB_H=1 -DHAVE_ZLIB=1 -DHAVE_HDF5_H=1 -DHAVE_HDF5=1
-DHAVE_H5GGET_NUM_OBJS=1 -DHAVE_FFTW3=1 -DHAVE_GLPK_GLPK_H=1 -DHAVE_GLPK=1
-DHAVE_CURL_CURL_H=1 -DHAVE_CURL=1 -DHAVE_MAGICK=1 -DHAVE_WINDOWS_H=1
-DHAVE_GL_GL_H=1 -DHAVE_GL_GLU_H=1 -DHAVE_OPENGL=1 -DHAVE_FTGL_FTGL_H=1
-DHAVE_FTGL=1 -DHAVE_FLTK=1 -DHAVE_IEEE754_DATA_FORMAT=1
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-DSIZEOF_SHORT=2 -DSIZEOF_INT=4 -DSIZEOF_LONG=4 -DSIZEOF_LONG_LONG=8
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-DHAVE_PTHREAD_H=1 -DHAVE_STDINT_H=1 -DHAVE_STDLIB_H=1 -DHAVE_STRING_H=1
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-DHAVE_CONIO_H=1 -DHAVE_ATEXIT=1 -DHAVE_BASENAME=1 -DHAVE_CHMOD=1
-DHAVE_DUP2=1 -DHAVE_EXECVP=1 -DHAVE_EXPM1=1 -DHAVE_EXPM1F=1 -DHAVE_FSTAT=1
-DHAVE_GETCWD=1 -DHAVE_GETPID=1 -DHAVE_GETTIMEOFDAY=1 -DHAVE__KBHIT=1
-DHAVE_LGAMMA=1 -DHAVE_LGAMMAF=1 -DHAVE_LOG1P=1 -DHAVE_LOG1PF=1
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-DHAVE_RMDIR=1 -DHAVE_ROUNDL=1 -DHAVE_SETLOCALE=1 -DHAVE_SETVBUF=1
-DHAVE_SNPRINTF=1 -DHAVE_STAT=1 -DHAVE_STRCASECMP=1 -DHAVE_STRDUP=1
-DHAVE_STRERROR=1 -DHAVE_STRICMP=1 -DHAVE_STRNCASECMP=1 -DHAVE_STRNICMP=1
-DHAVE_TEMPNAM=1 -DHAVE_TGAMMAF=1 -DHAVE_TRUNC=1 -DHAVE_UMASK=1
-DHAVE_UNLINK=1 -DHAVE_USLEEP=1 -DHAVE_UTIME=1 -DHAVE_VFPRINTF=1
-DHAVE_VSPRINTF=1 -DHAVE_VSNPRINTF=1 -DHAVE__CHMOD=1 -DHAVE__SNPRINTF=1
-DHAVE_DECL_EXP2=1 -DHAVE_DECL_ROUND=1 -DHAVE_DECL_TGAMMA=1 -DHAVE_EXP2=1
-DHAVE_ROUND=1 -DHAVE_TGAMMA=1 -DHAVE_MKSTEMPS=1 -DHAVE_C99_VSNPRINTF=1
-DOCTAVE_HAVE_BROKEN_STRPTIME=1 -D_WIN32_WINNT=0x0403 -DHAVE_LOADLIBRARY_API=1
-DENABLE_DYNAMIC_LINKING=1 -DHAVE_TIMEVAL=1 -DHAVE_CMATH_ISNAN=1
-DHAVE_CMATH_ISNANF=1 -DHAVE_CMATH_ISINF=1 -DHAVE_CMATH_ISINFF=1
-DHAVE_CMATH_ISFINITE=1 -DHAVE_CMATH_ISFINITEF=1 -DHAVE_FINITE=1
-DHAVE_ISNAN=1 -DHAVE_COPYSIGN=1 -DHAVE_SIGNBIT=1 -DHAVE__FINITE=1
-DHAVE__ISNAN=1 -DHAVE__COPYSIGN=1 -DHAVE_DECL_SIGNBIT=1 -DHAVE_ACOSH=1
-DHAVE_ACOSHF=1 -DHAVE_ASINH=1 -DHAVE_ASINHF=1 -DHAVE_ATANH=1 -DHAVE_ATANHF=1
-DHAVE_ERF=1 -DHAVE_ERFF=1 -DHAVE_ERFC=1 -DHAVE_ERFCF=1 -DHAVE_EXP2F=1
-DHAVE_LOG2=1 -DHAVE_LOG2F=1 -DHAVE_HYPOTF=1 -DHAVE_STRUCT_STAT_ST_RDEV=1
-DHAVE_DECL_TZNAME=1 -DHAVE_TZNAME=1 -DMKDIR_TAKES_ONE_ARG=1 -DUSE_READLINE=1
-DRETSIGTYPE=void -DHAVE_DECL_SYS_SIGLIST=0 -DMUST_REINSTALL_SIGHANDLERS=1
-DRETSIGTYPE_IS_VOID=1


User-preferences (please do not edit this section):

  EDITOR = C:\Octave\3.2.4_gcc-4.4.0\tools\notepad++\notepad++.exe
  EXEC_PATH =
C:\Octave\3.2.4_gcc-4.4.0\MINGW32\bin;C:\Octave\3.2.4_gcc-4.4.0\MSYS\bin;C:\Octave\3.2.4_gcc-4.4.0\libexec\octave\3.2.4\site\exec\i686-pc-mingw32;C:\Octave\3.2.4_gcc-4.4.0\libexec\octave\api-v37\site\exec\i686-pc-mingw32;C:\Octave\3.2.4_gcc-4.4.0\libexec\octave\site\exec\i686-pc-mingw32;C:\Octave\3.2.4_gcc-4.4.0\libexec\octave\3.2.4\exec\i686-pc-mingw32;C:\Octave\3.2.4_gcc-4.4.0\bin;C:\Program
Files\Common Files\Microsoft Shared\Windows Live;C:\Program Files (x86)\Common
Files\Microsoft Shared\Windows
Live;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;c:\Program
Files (x86)\Microsoft SQL Server\90\Tools\binn\;C:\Program Files (x86)\Windows
Live\Shared;C:\Program Files (x86)\OpenVPN\bin
  IMAGE_PATH = .;C:\Octave\3.2.4_gcc-4.4.0\share\octave\3.2.4\imagelib
  PAGER = C:\Octave\3.2.4_gcc-4.4.0\bin\less.exe
  PS1 = \s:\#> 
  PS2 = > 
  PS4 = + 
  beep_on_error = 0
  completion_append_char =  
  crash_dumps_octave_core = 1
  echo_executing_commands = 0
  fixed_point_format = 0
  gnuplot_binary = C:\Octave\3.2.4_gcc-4.4.0\bin\gnuplot.exe
# gnuplot_command_end = <no value or error in displaying it>
# gnuplot_command_plot = <no value or error in displaying it>
# gnuplot_command_replot = <no value or error in displaying it>
# gnuplot_command_splot = <no value or error in displaying it>
# gnuplot_command_title = <no value or error in displaying it>
# gnuplot_command_using = <no value or error in displaying it>
# gnuplot_command_with = <no value or error in displaying it>
  history_file = C:\Users\Kurt Strein\.octave_hist
  history_size = 1024
  ignore_function_time_stamp = system
  info_file = C:\Octave\3.2.4_gcc-4.4.0\share\info\octave.info
  info_program = info
  makeinfo_program = makeinfo
  max_recursion_depth = 256
  output_max_field_width = 5
  output_precision = 5
  page_output_immediately = 0
  page_screen_output = 1
# print_answer_id_name = <no value or error in displaying it>
  print_empty_dimensions = 1
  save_precision = 16
  saving_history = 1
  sighup_dumps_octave_core = 1
  sigterm_dumps_octave_core = 1
  silent_functions = 0
  split_long_rows = 1
  string_fill_char =  
  struct_levels_to_print = 2
  suppress_verbose_help_message = 0





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