Add grads for interpolate1d (#1742)

* add backprop for interpolate1d

* fix clippy lint

* correct fix clippy lint

candle-core/src/backprop.rs

@@ -113,7 +113,7 @@ impl Tensor {
                     | Op::Unary(_node, UnaryOp::Floor)
                     | Op::Unary(_node, UnaryOp::Round) => nodes,
                     Op::Reshape(node)
-                    | Op::UpsampleNearest1D(node)
+                    | Op::UpsampleNearest1D { arg: node, .. }
                     | Op::UpsampleNearest2D { arg: node, .. }
                     | Op::AvgPool2D { arg: node, .. }
                     | Op::MaxPool2D { arg: node, .. }
@@ -348,9 +348,18 @@ impl Tensor {
                         let sum_grad = grads.or_insert(arg)?;
                         *sum_grad = sum_grad.add(&grad_arg)?;
                     }
-                    Op::UpsampleNearest1D { .. } => Err(Error::BackwardNotSupported {
+                    Op::UpsampleNearest1D { arg, target_size } => {
-                        op: "upsample-nearest1d",
+                        let (_n, c, size) = arg.dims3()?;
-                    })?,
+                        if target_size % size != 0 {
+                            crate::bail!("backward not supported for non integer upscaling factors")
+                        }
+                        let scale = target_size / size;
+
+                        let kernel = Tensor::ones((c, 1, scale), arg.dtype(), arg.device())?;
+                        let conv_sum = grad.conv1d(&kernel, 0, scale, 1, c)?;
+                        let sum_grad = grads.or_insert(arg)?;
+                        *sum_grad = conv_sum;
+                    }
                     Op::UpsampleNearest2D {
                         arg,
                         target_h,

candle-core/src/op.rs

@@ -132,7 +132,10 @@ pub enum Op {
         stride: (usize, usize),
     },
 
-    UpsampleNearest1D(Tensor),
+    UpsampleNearest1D {
+        arg: Tensor,
+        target_size: usize,
+    },
     UpsampleNearest2D {
         arg: Tensor,
         target_h: usize,

candle-core/src/tensor.rs

@@ -1015,7 +1015,7 @@ impl Tensor {
     /// tensor also has three dimensions, `(batch, channels, target_size)`.
     pub fn interpolate1d(&self, target_size: usize) -> Result<Self> {
         let (n, c, _l) = self.dims3()?;
-        let op = BackpropOp::new1(self, Op::UpsampleNearest1D);
+        let op = BackpropOp::new1(self, |arg| Op::UpsampleNearest1D { arg, target_size });
         let storage = self
             .storage()
             .upsample_nearest1d(self.layout(), target_size)?;

candle-core/tests/grad_tests.rs

@@ -283,6 +283,39 @@ fn unary_grad(device: &Device) -> Result<()> {
         [1.0881, 0.9277, 1.0527, 0.5747],
     );
 
+    let x = Var::new(&[[[1f32, 2., 3.], [4., 5., 6.], [7., 8., 9.]]], device)?;
+    let y = x.interpolate1d(12)?.reshape(36)?;
+
+    println!("y: {}", y.unsqueeze(1)?);
+    #[rustfmt::skip]
+    let z = Tensor::new(
+        &[
+            1_f32, 02., 03., 04.,
+            05.,   06., 07., 08.,
+            09.,   10., 11., 12.,
+            13.,   14., 15., 16.,
+            17.,   18., 19., 20.,
+            21.,   22., 23., 24.,
+            25.,   26., 27., 28.,
+            29.,   30., 31., 32.,
+            33.,   34., 35., 36.,
+        ],
+        device,
+    )?;
+
+    let loss = y.unsqueeze(1)?.transpose(0, 1)?.matmul(&z.unsqueeze(1)?)?;
+
+    let grads = loss.backward()?;
+
+    let grad_x = grads.get(&x).context("no grad for x")?;
+
+    println!("grad: {grad_x}");
+
+    assert_eq!(
+        test_utils::to_vec3_round(grad_x, 4)?,
+        [[[10_f32, 26., 42.], [58., 74., 90.], [106., 122., 138.]]]
+    );
+
     // manually checked: see comments
     let x = Var::new(&[[[[1f32, 2., 3.], [4., 5., 6.], [7., 8., 9.]]]], device)?;
     let y = x.interpolate2d(6, 6)?.reshape(36)?;