chore: import upstream snapshot with attribution

books/PRML/PRML-master-Python/prml/nn/array/flatten.py

@@ -0,0 +1,28 @@
+from prml.nn.tensor.constant import Constant
+from prml.nn.tensor.tensor import Tensor
+from prml.nn.function import Function
+
+
+class Flatten(Function):
+    """
+    flatten array
+    """
+
+    def forward(self, x):
+        x = self._convert2tensor(x)
+        self._atleast_ndim(x, 2)
+        self.x = x
+        if isinstance(self.x, Constant):
+            return Constant(x.value.flatten())
+        return Tensor(x.value.flatten(), function=self)
+
+    def backward(self, delta):
+        dx = delta.reshape(*self.x.shape)
+        self.x.backward(dx)
+
+
+def flatten(x):
+    """
+    flatten N-dimensional array (N >= 2)
+    """
+    return Flatten().forward(x)