restrict test to reasonable values

python/tests/test_mechanics.py

@@ -129,10 +129,12 @@ class TestMechanics:
     @pytest.mark.parametrize('vectorized,single',[(mechanics.strain,strain)])
     def test_vectorize_strain(self,vectorized,single):
         F     = np.random.rand(self.n,3,3)
+        F     = np.einsum('...ij,...jk',F,F) # positive determinant
         F_vec = np.reshape(F,(self.n//10,10,3,3))
         t     = ['V','U'][np.random.randint(0,2)]
         m     = np.random.random()*10.0 -5.0
         for i,v in enumerate(np.reshape(vectorized(F_vec,t,m),vectorized(F,t,m).shape)):
+            if np.linalg.det(F[i]) < 1.e-10: continue
             assert np.allclose(single(F[i],t,m),v)
 
     @pytest.mark.parametrize('function',[mechanics.stress_Cauchy,