From c7f64eebd1f1e5d6a49b866a438014d7ff763332 Mon Sep 17 00:00:00 2001
From: michaelowenliu <liuyi.ntu@gmail.com>
Date: Thu, 27 Aug 2020 15:21:53 +0800
Subject: [PATCH] add comomon usages in models such as loss and prediction
 computing

---
 dygraph/models/model_utils.py | 102 ++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 dygraph/models/model_utils.py

diff --git a/dygraph/models/model_utils.py b/dygraph/models/model_utils.py
new file mode 100644
index 00000000..e0a88c35
--- /dev/null
+++ b/dygraph/models/model_utils.py
@@ -0,0 +1,102 @@
+# -*- encoding: utf-8 -*-
+# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn.functional as F
+from paddle import fluid
+from paddle.fluid import dygraph
+from paddle.fluid.dygraph import Conv2D
+from paddle.nn import SyncBatchNorm as BatchNorm
+
+from dygraph.models.architectures import layer_utils
+
+
+class FCNHead(fluid.dygraph.Layer):
+    """
+    The FCNHead implementation used in auxilary layer
+
+    Args:
+        in_channels (int): the number of input channels
+        out_channels (int): the number of output channels
+    """
+
+    def __init__(self, in_channels, out_channels):
+        super(FCNHead, self).__init__()
+
+        inter_channels = in_channels // 4
+        self.conv_bn_relu = layer_utils.ConvBnRelu(num_channels=in_channels,
+                                                   num_filters=inter_channels,
+                                                   filter_size=3,
+                                                   padding=1)
+
+        self.conv = Conv2D(num_channels=inter_channels,
+                           num_filters=out_channels,
+                           filter_size=1)
+
+    def forward(self, x):
+        x = self.conv_bn_relu(x)
+        x = F.dropout(x, p=0.1)
+        x = self.conv(x)
+        return x
+
+
+def get_loss(logit, label, ignore_index=255, EPS=1e-5):
+    """
+    compute forward loss of the model
+
+    Args:
+        logit (tensor): the logit of model output
+        label (tensor): ground truth
+
+    Returns:
+        avg_loss (tensor): forward loss
+    """
+    logit = fluid.layers.transpose(logit, [0, 2, 3, 1])
+    label = fluid.layers.transpose(label, [0, 2, 3, 1])
+    mask = label != ignore_index
+    mask = fluid.layers.cast(mask, 'float32')
+    loss, probs = fluid.layers.softmax_with_cross_entropy(
+        logit,
+        label,
+        ignore_index=ignore_index,
+        return_softmax=True,
+        axis=-1)
+
+    loss = loss * mask
+    avg_loss = paddle.mean(loss) / (paddle.mean(mask) + EPS)
+
+    label.stop_gradient = True
+    mask.stop_gradient = True
+
+    return avg_loss
+
+
+def get_pred_score_map(logit):
+    """
+    Get prediction and score map output in inference phase.
+
+    Args:
+        logit (tensor): output logit of network
+
+    Returns:
+        pred (tensor): predition map
+        score_map (tensor): score map
+    """
+    score_map = F.softmax(logit, axis=1)
+    score_map = fluid.layers.transpose(score_map, [0, 2, 3, 1])
+    pred = fluid.layers.argmax(score_map, axis=3)
+    pred = fluid.layers.unsqueeze(pred, axes=[3])
+
+    return pred, score_map
\ No newline at end of file
-- 
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