Ran autoconf to add fftw stuff to configure script

configure

@@ -719,6 +719,7 @@ enable_almost
 enable_gsl
 enable_xdrfile
 enable_boost_graph
+enable_fftw
 enable_openmp
 '
       ac_precious_vars='build_alias
@@ -1385,6 +1386,7 @@ Optional Features:
   --enable-gsl            enable search for gsl, default: no
   --enable-xdrfile        enable search for xdrfile, default: yes
   --enable-boost_graph    enable search for boost graph, default: no
+  --enable-fftw           enable search for fftw, default: no
   --disable-openmp        do not use OpenMP
 
 Some influential environment variables:
@@ -2868,6 +2870,24 @@ fi
 
 
 
+fftw=
+# Check whether --enable-fftw was given.
+if test "${enable_fftw+set}" = set; then :
+  enableval=$enable_fftw; case "${enableval}" in
+             (yes) fftw=true ;;
+             (no)  fftw=false ;;
+             (*)   as_fn_error $? "wrong argument to --enable-fftw" "$LINENO" 5 ;;
+  esac
+else
+  case "no" in
+             (yes) fftw=true ;;
+             (no)  fftw=false ;;
+  esac
+
+fi
+
+
+
 
 
 
@@ -6541,6 +6561,72 @@ fi
 $as_echo "$as_me: WARNING: cannot enable __PLUMED_HAS_BOOST_GRAPH" >&2;}
     fi
 
+fi
+if test $fftw == true ; then
+
+    found=ko
+    ac_fn_cxx_check_header_mongrel "$LINENO" "fftw3.h" "ac_cv_header_fftw3_h" "$ac_includes_default"
+if test "x$ac_cv_header_fftw3_h" = xyes; then :
+
+      ac_fn_cxx_check_func "$LINENO" "exit" "ac_cv_func_exit"
+if test "x$ac_cv_func_exit" = xyes; then :
+  found=ok
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for exit in -lfftw" >&5
+$as_echo_n "checking for exit in -lfftw... " >&6; }
+if ${ac_cv_lib_fftw_exit+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_check_lib_save_LIBS=$LIBS
+LIBS="-lfftw  $LIBS"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char exit ();
+int
+main ()
+{
+return exit ();
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  ac_cv_lib_fftw_exit=yes
+else
+  ac_cv_lib_fftw_exit=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+LIBS=$ac_check_lib_save_LIBS
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_fftw_exit" >&5
+$as_echo "$ac_cv_lib_fftw_exit" >&6; }
+if test "x$ac_cv_lib_fftw_exit" = xyes; then :
+  LIBS="-lfftw $LIBS" && found=ok
+fi
+
+
+fi
+
+
+fi
+
+
+    if test $found == ok ; then
+      $as_echo "#define __PLUMED_HAS_FFTW 1" >>confdefs.h
+
+    else
+       { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: cannot enable __PLUMED_HAS_FFTW" >&5
+$as_echo "$as_me: WARNING: cannot enable __PLUMED_HAS_FFTW" >&2;}
+    fi
+
 fi
 
 # in non-debug mode, add -DNDEBUG

developer-doc/plmdIntro.txt

@@ -465,4 +465,12 @@ you can use the exit funciton here, which should work even if you are using temp
 directive that appears around your library calling code and that we discussed earlier.  The last argument meanwhile is the name of the library - 
 the part that appears after the -l.  In the example above the code would thus try and link -llibrary_name. 
 
+Once you have made these edits issue the command:
+
+\verbatim
+autoconf
+\endverbatim
+
+and the necessary changes will be made to the configure script.  <b>You should never edit the configure script directly</b>
+
 */