add more examples

doc/design/graph_survey.md

@@ -15,7 +15,7 @@
 ```python
 def get_symbol(num_classes=10, **kwargs):
     data = mx.symbol.Variable('data')
-    data = mx.sym.Flatten(data=data)
+    data = mx.symbol.Flatten(data=data)
     fc1  = mx.symbol.FullyConnected(data = data, name='fc1', num_hidden=128)
     act1 = mx.symbol.Activation(data = fc1, name='relu1', act_type="relu")
     fc2  = mx.symbol.FullyConnected(data = act1, name = 'fc2', num_hidden = 64)
@@ -119,3 +119,113 @@ Expression的主要成员为ComputationGraph，可以在用户配置网络的过
 
 - 在用户配置网络时，所有的返回值都是Expression，包括最初的输入数据，及参数等
 - Expression已经包含了所有的依赖关系，可以被当做执行的target
+
+下面我们来看几个实例：
+
+- Mxnet
+
+
+```
+>>> import mxnet as mx
+>>> data = mx.symbol.Variable('data')
+>>> print data.debug_str()
+Variable:data
+
+>>> data = mx.symbol.Flatten(data=data)
+>>> print data.debug_str()
+Symbol Outputs:
+	output[0]=flatten0(0)
+Variable:data
+--------------------
+Op:Flatten, Name=flatten0
+Inputs:
+	arg[0]=data(0) version=0
+
+>>> fc1  = mx.symbol.FullyConnected(data = data, name='fc1', num_hidden=128)
+>>> print fc1.debug_str()
+Symbol Outputs:
+	output[0]=fc1(0)
+Variable:data
+--------------------
+Op:Flatten, Name=flatten0
+Inputs:
+	arg[0]=data(0) version=0
+Variable:fc1_weight
+Variable:fc1_bias
+--------------------
+Op:FullyConnected, Name=fc1
+Inputs:
+	arg[0]=flatten0(0)
+	arg[1]=fc1_weight(0) version=0
+	arg[2]=fc1_bias(0) version=0
+Attrs:
+	num_hidden=128
+
+```
+
+- TensorFlow
+
+```
+>>> import tensorflow as tf
+>>> c = tf.constant([[1.0, 2.0], [3.0, 4.0]])
+>>> print c.graph
+<tensorflow.python.framework.ops.Graph object at 0x10f256d50>
+>>> d = tf.constant([[1.0, 1.0], [0.0, 1.0]])
+>>> print d.graph
+<tensorflow.python.framework.ops.Graph object at 0x10f256d50>
+>>> e = tf.matmul(c, d)
+>>> print e.graph
+<tensorflow.python.framework.ops.Graph object at 0x10f256d50>
+```
+
+没有找到Graph的debug string接口，但是可以明确知道配置过程中只存在一个Graph。
+
+
+- dynet
+
+dynet可以在C++中书写配置
+
+```
+ComputationGraph cg;
+Expression W = parameter(cg, pW);
+cg.print_graphviz();
+
+Expression pred = W * xs[i];
+cg.print_graphviz();
+
+Expression loss = square(pred - ys[i]);
+cg.print_graphviz();
+```
+
+编译运行后，得到打印结果：
+
+```
+# first print
+digraph G {
+  rankdir=LR;
+  nodesep=.05;
+  N0 [label="v0 = parameters({1}) @ 0x7ffe4de00110"];
+}
+# second print
+digraph G {
+  rankdir=LR;
+  nodesep=.05;
+  N0 [label="v0 = parameters({1}) @ 0x7ffe4de00110"];
+  N1 [label="v1 = v0 * -0.98"];
+  N0 -> N1;
+}
+# third print
+digraph G {
+  rankdir=LR;
+  nodesep=.05;
+  N0 [label="v0 = parameters({1}) @ 0x7ffe4de00110"];
+  N1 [label="v1 = v0 * -0.98"];
+  N0 -> N1;
+  N2 [label="v2 = -1.88387 - v1"];
+  N1 -> N2;
+  N3 [label="v3 = -v2"];
+  N2 -> N3;
+  N4 [label="v4 = square(v3)"];
+  N3 -> N4;
+}
+```