fix #54

Author: refraction-ray

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 - Add sparse matrix related methods for pytorch backend.
 
+- Add exp and expm for torch backend.
+
 ## v1.4.0
 
 ### Added

tensorcircuit/backends/pytorch_backend.py

@@ -229,6 +229,9 @@ def ones(self, shape: Tuple[int, ...], dtype: Optional[str] = None) -> Tensor:
         r = torchlib.ones(shape)
         return self.cast(r, dtype)
 
+    def exp(self, tensor: Tensor) -> Tensor:
+        return torchlib.exp(tensor)
+
     def zeros(self, shape: Tuple[int, ...], dtype: Optional[str] = None) -> Tensor:
         if dtype is None:
             dtype = dtypestr
@@ -248,7 +251,8 @@ def convert_to_tensor(self, tensor: Tensor, dtype: Optional[str] = None) -> Tens
         return result
 
     def expm(self, a: Tensor) -> Tensor:
-        raise NotImplementedError("pytorch backend doesn't support expm")
+        return torchlib.linalg.matrix_exp(a)
+        # raise NotImplementedError("pytorch backend doesn't support expm")
         # in 2020, torch has no expm, hmmm. but that's ok,
         # it doesn't support complex numbers which is more severe issue.
         # see https://github.com/pytorch/pytorch/issues/9983

tests/test_backends.py

@@ -305,6 +305,14 @@ def sum_(carry, x):
 def test_backend_methods_2(backend):
     np.testing.assert_allclose(tc.backend.mean(tc.backend.ones([10])), 1.0, atol=1e-5)
     # acos acosh asin asinh atan atan2 atanh cosh (cos) tan tanh sinh (sin)
+    np.testing.assert_allclose(
+        tc.backend.exp(tc.backend.ones([2, 3])), np.exp(np.ones([2, 3])), atol=1e-5
+    )
+    np.testing.assert_allclose(
+        tc.backend.expm(tc.backend.ones([3, 3])),
+        scipy.linalg.expm(np.ones([3, 3])),
+        atol=1e-5,
+    )
     np.testing.assert_allclose(
         tc.backend.acos(tc.backend.ones([2], dtype="float32")),
         np.arccos(tc.backend.ones([2])),