title: Installing rb-gsl gem using Cygwin
body: <p>I'm having issues installing rb-gsl under Windows using Cygwin. I'm using the RubyInstaller for Windows with the dev kit installed. I've installed Cygwin and the GSL runtime, gsl-apps, gsl-devel and gsl-doc packages. When issuing a gem install command I get the following:</p>
  
  <pre><code>$ gem.bat install "C:\Documents and Settings\jzh3fd.2UA1071FGF\Desktop\gsl-1.14
  .7.gem"
  Temporarily enhancing PATH to include DevKit...
  Building native extensions.  This could take a while...
  ERROR:  Error installing C:\Documents and Settings\jzh3fd.2UA1071FGF\Desktop\gsl
  -1.14.7.gem:
          ERROR: Failed to build gem native extension.
  
          C:/Ruby192/bin/ruby.exe extconf.rb
  checking gsl version... 1.14
  checking gsl cflags... -I/usr/include
  checking for main() in -lcblas... no
  checking gsl libs... -L/usr/lib -lgsl -lgslcblas -lm
  checking for round()... no
  checking for rngextra/rngextra.h... no
  checking for qrngextra/qrngextra.h... no
  checking for ool/ool_version.h... no
  checking for tensor/tensor.h... no
  checking for jacobi.h... no
  checking for gsl/gsl_cqp.h... no
  checking for gsl/gsl_multimin_fsdf.h... no
  checking for gsl_poly_solve_quartic() in -lgsl... no
  checking for gsl_eigen_francis() in -lgsl... no
  checking for ndlinear/gsl_multifit_ndlinear.h... no
  checking for alf/alf.h... no
  checking rb-gsl version...1.14.7
  checking ruby version... 1.9.2
  checking for graph... no
  checking for narray.h... yes
  checking for main() in -lnarray... no
  checking for tamu_anova/tamu_anova.h... no
  checking for main() in -ltamuanova... no
  creating Makefile
  
  make
  C:/Ruby192/bin/ruby -e "puts 'EXPORTS', 'Init_rb_gsl'"  &gt; rb_gsl-i386-mingw32.de
  f
  gcc -I. -IC:/Ruby192/include/ruby-1.9.1/i386-mingw32 -I/C/Ruby192/include/ruby-1
  .9.1/ruby/backward -I/C/Ruby192/include/ruby-1.9.1 -I. -DHAVE_NARRAY_H  -IC:/Rub
  y192/lib/ruby/gems/1.9.1/gems/narray-0.5.9.9/. -IC:/Ruby192/lib/ruby/site_ruby/1
  .9.1/i386-msvcrt    -Wall -I../include  -I/usr/include  -o alf.o -c alf.c
  gcc -I. -IC:/Ruby192/include/ruby-1.9.1/i386-mingw32 -I/C/Ruby192/include/ruby-1
  .9.1/ruby/backward -I/C/Ruby192/include/ruby-1.9.1 -I. -DHAVE_NARRAY_H  -IC:/Rub
  y192/lib/ruby/gems/1.9.1/gems/narray-0.5.9.9/. -IC:/Ruby192/lib/ruby/site_ruby/1
  .9.1/i386-msvcrt    -Wall -I../include  -I/usr/include  -o array.o -c array.c
  In file included from array.c:14:0:
  ../include/rb_gsl_common.h:18:27: fatal error: gsl/gsl_errno.h: No such file or
  directory
  compilation terminated.
  make: *** [array.o] Error 1
  
  
  Gem files will remain installed in C:/Ruby192/lib/ruby/gems/1.9.1/gems/gsl-1.14.
  7 for inspection.
  Results logged to C:/Ruby192/lib/ruby/gems/1.9.1/gems/gsl-1.14.7/ext/gem_make.ou
  t
  </code></pre>
  
  <p>I have checked and I can find gsl_errno.h at /usr/include/gsl</p>