Add the continuous method.

src/error.rs

@@ -12,6 +12,9 @@ pub enum Error {
     #[error("{op} expects at least one tensor")]
     OpRequiresAtLeastOneTensor { op: &'static str },
 
+    #[error("backward is not supported for {op}")]
+    BackwardNotSupported { op: &'static str },
+
     #[error("the candle crate has not been built with cuda support")]
     NotCompiledWithCudaSupport,
 

src/op.rs

@@ -17,6 +17,8 @@ pub(crate) enum Op {
         add: f64,
     },
     Neg(Tensor),
+    #[allow(dead_code)]
+    Reshape(Tensor),
     Sqr(Tensor),
     Sqrt(Tensor),
     ToDevice(Tensor),

src/tensor.rs

@@ -575,6 +575,26 @@ impl Tensor {
         }
     }
 
+    pub fn contiguous(&self) -> Result<Tensor> {
+        if self.is_contiguous() {
+            Ok(self.clone())
+        } else {
+            let shape = self.shape();
+            let mut storage = self.device().zeros(shape, self.dtype())?;
+            self.storage
+                .copy_strided_src(&mut storage, shape, &self.stride, 0)?;
+            let tensor_ = Tensor_ {
+                id: TensorId::new(),
+                storage,
+                shape: shape.clone(),
+                stride: shape.stride_contiguous(),
+                op: self.op.clone(),
+                is_variable: self.is_variable,
+            };
+            Ok(Tensor(Arc::new(tensor_)))
+        }
+    }
+
     pub fn cat(args: &[Self], dim: usize) -> Result<Self> {
         if args.is_empty() {
             return Err(Error::OpRequiresAtLeastOneTensor { op: "cat" });
@@ -708,7 +728,8 @@ impl Tensor {
                             nodes
                         }
                     }
-                    Op::ToDevice(node)
+                    Op::Reshape(node)
+                    | Op::ToDevice(node)
                     | Op::Transpose(node, _, _)
                     | Op::Sqr(node)
                     | Op::Sqrt(node)
@@ -788,9 +809,7 @@ impl Tensor {
                         let rhs_sum_grad = grads.or_insert(rhs)?;
                         *rhs_sum_grad = rhs_sum_grad.add(&rhs_grad)?;
                     }
-                    Op::Cat(_args, _dim) => {
+                    Op::Cat(_args, _dim) => return Err(Error::BackwardNotSupported { op: "cat" }),
-                        todo!()
-                    }
                     Op::Affine { arg, mul, .. } => {
                         let arg_grad = grad.affine(*mul, 0.)?;
                         let sum_grad = grads.or_insert(arg)?;
@@ -801,6 +820,7 @@ impl Tensor {
                         let sum_grad = grads.or_insert(arg)?;
                         *sum_grad = sum_grad.add(&arg_grad)?
                     }
+                    Op::Reshape(_arg) => return Err(Error::BackwardNotSupported { op: "reshape" }),
                     Op::Sqr(arg) => {
                         let arg_grad = arg.mul(&grad)?.affine(2., 0.)?;
                         let sum_grad = grads.or_insert(arg)?;