add doc and reimplement Dim::truncate (clab#970)

* remote use GPU:0 by default when use --dynet-gpu

* fix error

* Comment DeviceMempool enum

* clab#945
1. add doc for Dim::truncate
2. reimplement Dim::truncate
3. add tests for dim

dynet/dim.h

@@ -118,16 +118,14 @@ struct Dim {
     return p;
   }
   /**
-   * \brief [TODO]
-   * \details [long description]
-   * \return [description]
+   * \brief remove trailing dimensions of 1
+   * \details iterate all the dimensions of Dim, stop at last dimension of 1
+   * \return truncated dimension
    */
   inline Dim truncate() const {
     Dim r = *this;
-    unsigned int m = 1;
-    unsigned int s = size();
-    for (unsigned int i = 1; i < s; ++i)
-      if (size(i) > 1) m = i + 1;
+    unsigned int m = nd;
+    while (m > 1 && size(m-1) == 1) --m;
     r.resize(m);
     return r;
   }

tests/CMakeLists.txt

@@ -9,7 +9,7 @@ if (DEFINED ENV{DYNET_TEST_DEVICES})  # use env variable as preprocessor macro
   add_definitions(-DDYNET_TEST_DEVICES=$ENV{DYNET_TEST_DEVICES})
 endif()
 
-foreach(TESTNAME dynet exec io mem nodes params tensor trainers rnn softmax)
+foreach(TESTNAME dim dynet exec io mem nodes params tensor trainers rnn softmax)
   add_executable(test-${TESTNAME} test-${TESTNAME}.cc)
   if (NOT MSVC)
     target_link_libraries(test-${TESTNAME} ${Boost_LIBRARIES} ${CMAKE_DL_LIBS})

tests/test-dim.cc

@@ -0,0 +1,40 @@
+#define BOOST_TEST_MODULE TEST_DIM
+
+#include <dynet/dim.h>
+
+#include "test.h"
+
+using namespace dynet;
+
+struct DimTest {
+
+};
+
+BOOST_FIXTURE_TEST_SUITE(dim_test, DimTest);
+
+BOOST_AUTO_TEST_CASE( test_dim_truncate_no_trailing_one ) {
+    Dim d1({1,3,4});
+    Dim t1 = d1.truncate();
+    BOOST_CHECK_EQUAL(t1.nd, 3);
+}
+
+BOOST_AUTO_TEST_CASE( test_dim_truncate_all_one ) {
+    Dim d1({1,1,1});
+    Dim t1 = d1.truncate();
+    BOOST_CHECK_EQUAL(t1.nd, 1);
+}
+
+BOOST_AUTO_TEST_CASE( test_dim_truncate_trailing_one ) {
+    Dim d1({4,3,1});
+    Dim t1 = d1.truncate();
+    BOOST_CHECK_EQUAL(t1.nd, 2);
+}
+
+BOOST_AUTO_TEST_CASE( test_dim_truncate_multiple_one ) {
+    Dim d1({4,1,1});
+    Dim t1 = d1.truncate();
+    BOOST_CHECK_EQUAL(t1.nd, 1);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+