Some fixes for yolo-v3. (#529)

* Some fixes for yolo-v3.

* Use the running stats for inference in the batch-norm layer.

* Get some proper predictions for yolo.

* Avoid the quadratic insertion.

candle-nn/src/batch_norm.rs

@@ -40,6 +40,8 @@ impl From<f64> for BatchNormConfig {
 
 #[derive(Debug)]
 pub struct BatchNorm {
+    running_mean: Tensor,
+    running_var: Tensor,
     weight_and_bias: Option<(Tensor, Tensor)>,
     remove_mean: bool,
     eps: f64,
@@ -47,7 +49,14 @@ pub struct BatchNorm {
 }
 
 impl BatchNorm {
-    pub fn new(num_features: usize, weight: Tensor, bias: Tensor, eps: f64) -> Result<Self> {
+    pub fn new(
+        num_features: usize,
+        running_mean: Tensor,
+        running_var: Tensor,
+        weight: Tensor,
+        bias: Tensor,
+        eps: f64,
+    ) -> Result<Self> {
         if eps < 0. {
             candle::bail!("batch-norm eps cannot be negative {eps}")
         }
@@ -64,6 +73,8 @@ impl BatchNorm {
             )
         }
         Ok(Self {
+            running_mean,
+            running_var,
             weight_and_bias: Some((weight, bias)),
             remove_mean: true,
             eps,
@@ -71,11 +82,18 @@ impl BatchNorm {
         })
     }
 
-    pub fn new_no_bias(num_features: usize, eps: f64) -> Result<Self> {
+    pub fn new_no_bias(
+        num_features: usize,
+        running_mean: Tensor,
+        running_var: Tensor,
+        eps: f64,
+    ) -> Result<Self> {
         if eps < 0. {
             candle::bail!("batch-norm eps cannot be negative {eps}")
         }
         Ok(Self {
+            running_mean,
+            running_var,
             weight_and_bias: None,
             remove_mean: true,
             eps,
@@ -84,8 +102,8 @@ impl BatchNorm {
     }
 }
 
-impl crate::Module for BatchNorm {
-    fn forward(&self, x: &Tensor) -> Result<Tensor> {
+impl BatchNorm {
+    pub fn forward_learning(&self, x: &Tensor) -> Result<Tensor> {
         let x_dtype = x.dtype();
         let internal_dtype = match x_dtype {
             DType::F16 | DType::BF16 => DType::F32,
@@ -129,6 +147,29 @@ impl crate::Module for BatchNorm {
     }
 }
 
+impl crate::Module for BatchNorm {
+    fn forward(&self, x: &Tensor) -> Result<Tensor> {
+        let target_shape: Vec<usize> = x
+            .dims()
+            .iter()
+            .enumerate()
+            .map(|(idx, v)| if idx == 1 { *v } else { 1 })
+            .collect();
+        let target_shape = target_shape.as_slice();
+        let x = x
+            .broadcast_sub(&self.running_mean.reshape(target_shape)?)?
+            .broadcast_div(&(self.running_var.reshape(target_shape)? + self.eps)?.sqrt()?)?;
+        match &self.weight_and_bias {
+            None => Ok(x),
+            Some((weight, bias)) => {
+                let weight = weight.reshape(target_shape)?;
+                let bias = bias.reshape(target_shape)?;
+                x.broadcast_mul(&weight)?.broadcast_add(&bias)
+            }
+        }
+    }
+}
+
 pub fn batch_norm<C: Into<BatchNormConfig>>(
     num_features: usize,
     config: C,
@@ -138,6 +179,8 @@ pub fn batch_norm<C: Into<BatchNormConfig>>(
     if config.eps < 0. {
         candle::bail!("batch-norm eps cannot be negative {}", config.eps)
     }
+    let running_mean = vb.get_or_init(num_features, "running_mean", crate::Init::Const(0.))?;
+    let running_var = vb.get_or_init(num_features, "running_var", crate::Init::Const(1.))?;
     let weight_and_bias = if config.affine {
         let weight = vb.get_or_init(num_features, "weight", crate::Init::Const(1.))?;
         let bias = vb.get_or_init(num_features, "bias", crate::Init::Const(0.))?;
@@ -146,6 +189,8 @@ pub fn batch_norm<C: Into<BatchNormConfig>>(
         None
     };
     Ok(BatchNorm {
+        running_mean,
+        running_var,
         weight_and_bias,
         remove_mean: config.remove_mean,
         eps: config.eps,