Add the reshape method and operation (without grad for now).

src/op.rs

@@ -17,7 +17,6 @@ pub(crate) enum Op {
         add: f64,
     },
     Neg(Tensor),
-    #[allow(dead_code)]
     Reshape(Tensor),
     Sqr(Tensor),
     Sqrt(Tensor),

src/tensor.rs

@@ -595,6 +595,36 @@ impl Tensor {
         }
     }
 
+    // TODO: Do we want to allow target shape using -1 on some dimensions?
+    pub fn reshape<S: Into<Shape>>(&self, shape: S) -> Result<Tensor> {
+        let shape = shape.into();
+        if shape.elem_count() != self.elem_count() {
+            return Err(Error::ShapeMismatchBinaryOp {
+                lhs: self.shape().clone(),
+                rhs: shape,
+                op: "reshape",
+            });
+        }
+        let mut storage = self.device().zeros(&shape, self.dtype())?;
+        self.storage
+            .copy_strided_src(&mut storage, &shape, &self.stride, 0)?;
+        let op = if self.track_op() {
+            Some(Op::Reshape(self.clone()))
+        } else {
+            None
+        };
+        let stride = shape.stride_contiguous();
+        let tensor_ = Tensor_ {
+            id: TensorId::new(),
+            storage,
+            shape,
+            stride,
+            op,
+            is_variable: false,
+        };
+        Ok(Tensor(Arc::new(tensor_)))
+    }
+
     pub fn cat(args: &[Self], dim: usize) -> Result<Self> {
         if args.is_empty() {
             return Err(Error::OpRequiresAtLeastOneTensor { op: "cat" });