fixed output_list | now it has only 5 elements instead of 5*batchsize (#2914)

* fixed the  output_list | now it has only 5 elements instead of 5*batch_size

* Update ignite/metrics/ssim.py

batch_size variable instead of using y_pred.size(0) directly

Co-authored-by: vfdev <[email protected]>

---------

Co-authored-by: vfdev <[email protected]>

Author: moienr

ignite/metrics/ssim.py

@@ -159,10 +159,10 @@ def update(self, output: Sequence[torch.Tensor]) -> None:
         y_pred = F.pad(y_pred, [self.pad_w, self.pad_w, self.pad_h, self.pad_h], mode="reflect")
         y = F.pad(y, [self.pad_w, self.pad_w, self.pad_h, self.pad_h], mode="reflect")
 
-        input_list = torch.cat([y_pred, y, y_pred * y_pred, y * y, y_pred * y])
-        outputs = F.conv2d(input_list, self._kernel, groups=channel)
-
-        output_list = [outputs[x * y_pred.size(0) : (x + 1) * y_pred.size(0)] for x in range(len(outputs))]
+        input_list = [y_pred, y, y_pred * y_pred, y * y, y_pred * y]
+        outputs = F.conv2d(torch.cat(input_list), self._kernel, groups=channel)
+        batch_size = y_pred.size(0)
+        output_list = [outputs[x * batch_size : (x + 1) * batch_size] for x in range(len(input_list))]
 
         mu_pred_sq = output_list[0].pow(2)
         mu_target_sq = output_list[1].pow(2)