Add inner / outer op (#348)

* inner / outer impl

* python tests

* ops list and ack

* updated descriptions

* use test helper

* removed dtype check and flatten outer to 1-D

* updated docs

* just use the reshape to flatten

tests/ops_tests.cpp

@@ -2315,3 +2315,47 @@ TEST_CASE("tensordot") {
       {3, 6});
   CHECK(array_equal(z, expected).item<bool>());
 }
+
+TEST_CASE("outer") {
+  auto x = arange(1.0, 5.0);
+  auto y = arange(1.0, 4.0);
+  auto z = outer(x, y);
+  auto expected = array(
+      {1.0, 2.0, 3.0, 2.0, 4.0, 6.0, 3.0, 6.0, 9.0, 4.0, 8.0, 12.0}, {4, 3});
+  CHECK(array_equal(z, expected).item<bool>());
+
+  x = ones({5});
+  y = linspace(-2., 2., 5);
+  z = outer(x, y);
+  expected = array(
+      {-2., -1., 0.,  1.,  2., -2., -1., 0.,  1.,  2., -2., -1., 0.,
+       1.,  2.,  -2., -1., 0., 1.,  2.,  -2., -1., 0., 1.,  2.},
+      {5, 5});
+  CHECK(array_equal(z, expected).item<bool>());
+}
+
+TEST_CASE("inner") {
+  CHECK_THROWS_AS(
+      inner(reshape(arange(5.), {1, 5}), reshape(arange(6.), {2, 3})),
+      std::invalid_argument);
+  auto x = array({1., 2., 3.});
+  auto y = array({0., 1., 0.});
+  auto z = inner(x, y);
+  CHECK_EQ(z.item<float>(), 2.f);
+
+  x = reshape(arange(24.), {2, 3, 4});
+  y = arange(4.);
+  z = inner(x, y);
+  auto expected = array({14., 38., 62., 86., 110., 134.}, {2, 3});
+  CHECK(array_equal(z, expected).item<bool>());
+
+  x = reshape(arange(2.), {1, 1, 2});
+  y = reshape(arange(6.), {3, 2});
+  z = inner(x, y);
+  expected = array({1., 3., 5.}, {1, 1, 3});
+  CHECK(array_equal(z, expected).item<bool>());
+
+  z = inner(eye(2), array(7.));
+  expected = array({7., 0., 0., 7.}, {2, 2});
+  CHECK(array_equal(z, expected).item<bool>());
+}