Trac #33751: random doctest failure in src/sage/matrix/matrix_integer…

…_dense_hnf.py

Part of #32544:

{{{#!sage
sage -t --random-seed=47467259736041671371069989299524409608
src/sage/matrix/matrix_integer_dense_hnf.py
**********************************************************************
File "src/sage/matrix/matrix_integer_dense_hnf.py", line 1240, in
sage.matrix.matrix_integer_dense_hnf.?
Failed example:
    matrix_integer_dense_hnf.sanity_checks(times=5,
check_using_magma=False)
Exception raised:
    Traceback (most recent call last):
      File "~/sage/src/sage/doctest/forker.py", line 695, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "~/sage/src/sage/doctest/forker.py", line 1093, in
compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.matrix.matrix_integer_dense_hnf.?[1]>", line
1, in <module>
        matrix_integer_dense_hnf.sanity_checks(times=Integer(5),
check_using_magma=False)
      File "~/sage/src/sage/matrix/matrix_integer_dense_hnf.py", line
1285, in sanity_checks
        __do_check([random_matrix(ZZ, n, m, x=-2**32, y=2**32)
      File "~/sage/src/sage/matrix/matrix_integer_dense_hnf.py", line
1276, in __do_check
        if hnf(a)[0] != a.echelon_form(algorithm='pari'):
      File "~/sage/src/sage/matrix/matrix_integer_dense_hnf.py", line
1106, in hnf
        H, pivots = probable_hnf(A, include_zero_rows=include_zero_rows,
      File "~/sage/src/sage/matrix/matrix_integer_dense_hnf.py", line
926, in probable_hnf
        H = hnf_square(C, proof=proof)
      File "~/sage/src/sage/matrix/matrix_integer_dense_hnf.py", line
568, in hnf_square
        raise ValueError("A must be square.")
    ValueError: A must be square.
**********************************************************************
}}}

(From a patchbot run in #33619.)

URL: https://trac.sagemath.org/33751
Reported by: lorenz
Ticket author(s): Jonathan Kliem
Reviewer(s): Kevin Lui

src/sage/matrix/matrix_integer_dense_hnf.py

@@ -1103,13 +1103,18 @@ def hnf(A, include_zero_rows=True, proof=True):
             return H.matrix_from_rows(range(len(pivots))), pivots
 
     while True:
-        H, pivots = probable_hnf(A, include_zero_rows=include_zero_rows,
+        try:
+            H, pivots = probable_hnf(A, include_zero_rows=include_zero_rows,
                                  proof=True)
+        except ValueError:
+            verbose("The attempt failed since the pivots must have been wrong. We try again.")
+            continue
+
         if is_in_hnf_form(H, pivots):
             if not include_zero_rows and len(pivots) > H.nrows():
                 H = H.matrix_from_rows(range(len(pivots)))
             return H, pivots
-        verbose("After attempt the return matrix is not in HNF form since pivots must have been wrong.  We try again.")
+        verbose("After attempt the return matrix is not in HNF form since pivots must have been wrong. We try again.")
 
 
 def hnf_with_transformation(A, proof=True):