add kmax pooling module

fastNLP/modules/convolution/kmax_pool.py

@@ -0,0 +1,20 @@
+# python: 3.6
+# encoding: utf-8
+
+import torch
+import torch.nn as nn
+# import torch.nn.functional as F
+
+
+class KMaxPool(nn.Module):
+    """K max-pooling module."""
+
+    def __init__(self, k):
+        super(KMaxPool, self).__init__()
+        self.k = k
+
+    def forward(self, x):
+        # [N,C,L] -> [N,C*k]
+        x, index = torch.topk(x, self.k, dim=-1, sorted=False)
+        x = torch.reshape(x, (x.size(0), -1))
+        return x