Add preliminary detection of UMFPACK library (and headers).

configure.ac

@@ -32,6 +32,10 @@ AX_LAPACK
 # Checks for header files.
 AC_CHECK_HEADERS([float.h limits.h stddef.h stdlib.h string.h])
 
+AC_CHECK_HEADERS([suitesparse/umfpack.h],
+                 [umfpack_header=yes],
+                 [umfpack_header=no])
+
 # Checks for typedefs, structures, and compiler characteristics.
 AC_HEADER_STDBOOL
 AC_TYPE_SIZE_T
@@ -40,6 +44,16 @@ AC_CHECK_TYPES([ptrdiff_t])
 # Checks for library functions.
 AC_CHECK_FUNCS([floor memmove pow sqrt strchr strtol])
 
+AC_SEARCH_LIBS([umfpack_dl_solve], [umfpack],
+               [umfpack_lib=yes], [umfpack_lib=no])
+
+AM_CONDITIONAL([UMFPACK],
+  [test "x$umfpack_header" != "xno" -a "x$umfpack_lib" != "xno"])
+
+AM_COND_IF([UMFPACK], [],
+[AC_MSG_NOTICE([Found no working installation of UMFPACK.
+                UMFPACK support is disabled.])])
+
 AC_CONFIG_FILES([
  Makefile
  tests/Makefile