BUG,ENH: allow linalg.cond to work on a stack of matrices

This was buggy, because the underlying functions supported it
partially but cond was not aware of this.

Closes gh-6351

1 files changed, 12 insertions, 2 deletions

diff --git a/numpy/linalg/tests/test_linalg.py b/numpy/linalg/tests/test_linalg.py
index aedcc6a95..7c577d86f 100644
--- a/numpy/linalg/tests/test_linalg.py
+++ b/numpy/linalg/tests/test_linalg.py
@@ -556,7 +556,12 @@ class TestCondSVD(LinalgTestCase, LinalgGeneralizedTestCase):
     def do(self, a, b):
         c = asarray(a)  # a might be a matrix
         s = linalg.svd(c, compute_uv=False)
-        old_assert_almost_equal(s[0] / s[-1], linalg.cond(a), decimal=5)
+        old_assert_almost_equal(
+            s[..., 0] / s[..., -1], linalg.cond(a), decimal=5)
+
+    def test_stacked_arrays_explicitly(self):
+        A = np.array([[1., 2., 1.], [0, -2., 0], [6., 2., 3.]])
+        assert_equal(linalg.cond(A), linalg.cond(A[None, ...])[0])
 
 
 class TestCond2(LinalgTestCase):
@@ -564,7 +569,12 @@ class TestCond2(LinalgTestCase):
     def do(self, a, b):
         c = asarray(a)  # a might be a matrix
         s = linalg.svd(c, compute_uv=False)
-        old_assert_almost_equal(s[0] / s[-1], linalg.cond(a, 2), decimal=5)
+        old_assert_almost_equal(
+            s[..., 0] / s[..., -1], linalg.cond(a, 2), decimal=5)
+
+    def test_stacked_arrays_explicitly(self):
+        A = np.array([[1., 2., 1.], [0, -2., 0], [6., 2., 3.]])
+        assert_equal(linalg.cond(A, 2), linalg.cond(A[None, ...], 2)[0])
 
 
 class TestCondInf(object):