Merge pull request #1714 from wjmaddox/stable_qr_fix

Force add to zero sign in stable_qr

Author: Balandat

gpytorch/utils/qr.py

@@ -26,6 +26,9 @@ def stable_qr(mat):
     if torch.any(zeroish):
         # can't use in-place operation here b/c it would mess up backward pass
         # haven't found a more elegant way to add a jitter diagonal yet...
-        jitter_diag = 1e-6 * torch.sign(Rdiag) * zeroish.to(Rdiag)
+        Rdiag_sign = torch.sign(Rdiag)
+        # force zero diagonals to have jitter added to them.
+        Rdiag_sign[Rdiag_sign == 0] = 1.0
+        jitter_diag = 1e-6 * Rdiag_sign * zeroish.to(Rdiag)
         R = R + torch.diag_embed(jitter_diag)
     return Q, R