Disable use of linbox charpoly/minpoly on 64-bit computers.

Author: williamstein

src/sage/matrix/matrix_integer_dense.pyx

@@ -66,6 +66,9 @@ from sage.libs.linbox.linbox cimport Linbox_integer_dense
 cdef Linbox_integer_dense linbox
 linbox = Linbox_integer_dense()
 
+import sage.misc.misc
+USE_LINBOX_POLY = not sage.misc.misc.is_64bit()
+
 cdef class Matrix_integer_dense(matrix_dense.Matrix_dense):   # dense or sparse
     r"""
     Matrix over the integers.
@@ -661,7 +664,8 @@ cdef class Matrix_integer_dense(matrix_dense.Matrix_dense):   # dense or sparse
             algorithm -- 'linbox' (default)
                          'generic'
 
-        NOTE: Linbox only used on Darwin OS X right now.
+        NOTE: Linbox charpoly disabled on 64-bit machines, since it
+        hangs in many cases.
 
         EXAMPLES:
             sage: A = matrix(ZZ,6, range(36))
@@ -679,6 +683,9 @@ cdef class Matrix_integer_dense(matrix_dense.Matrix_dense):   # dense or sparse
         x = self.fetch(key)
         if x: return x
 
+        if algorithm == 'linbox' and not USE_LINBOX_POLY:
+            algorithm = 'generic'
+
         if algorithm == 'linbox':
             g = self._charpoly_linbox(var)
         elif algorithm == 'generic':
@@ -696,7 +703,8 @@ cdef class Matrix_integer_dense(matrix_dense.Matrix_dense):   # dense or sparse
             algorithm -- 'linbox' (default)
                          'generic'
 
-        NOTE: Linbox only used on Darwin OS X right now.
+        NOTE: Linbox charpoly disabled on 64-bit machines, since it
+        hangs in many cases.
 
         EXAMPLES:
             sage: A = matrix(ZZ,6, range(36))
@@ -710,6 +718,9 @@ cdef class Matrix_integer_dense(matrix_dense.Matrix_dense):   # dense or sparse
         x = self.fetch(key)
         if x: return x
 
+        if algorithm == 'linbox' and not USE_LINBOX_POLY:
+            algorithm = 'generic'
+
         if algorithm == 'linbox':
             g = self._minpoly_linbox(var)
         elif algorithm == 'generic':