C++ autograd example

autograd.cpp contains several examples of doing autograd in PyTorch C++ frontend.

To build the code, run the following commands from your terminal:

$ cd autograd
$ mkdir build
$ cd build
$ cmake -DCMAKE_PREFIX_PATH=/path/to/libtorch ..
$ make

where /path/to/libtorch should be the path to the unzipped LibTorch distribution, which you can get from the PyTorch homepage.

Execute the compiled binary to run:

$ ./autograd
====== Running: "Basic autograd operations" ======
 1  1
 1  1
[ CPUFloatType{2,2} ]
 3  3
 3  3
[ CPUFloatType{2,2} ]
AddBackward1
 27  27
 27  27
[ CPUFloatType{2,2} ]
MulBackward1
27
[ CPUFloatType{} ]
MeanBackward0
false
true
SumBackward0
 4.5000  4.5000
 4.5000  4.5000
[ CPUFloatType{2,2} ]
  813.6625
 1015.0142
 -664.8849
[ CPUFloatType{3} ]
MulBackward1
  204.8000
 2048.0000
    0.2048
[ CPUFloatType{3} ]
true
true
false
true
false
true

====== Running "Computing higher-order gradients in C++" ======
 0.0025  0.0946  0.1474  0.1387
 0.0238 -0.0018  0.0259  0.0094
 0.0513 -0.0549 -0.0604  0.0210
[ CPUFloatType{3,4} ]

====== Running "Using custom autograd function in C++" ======
-3.5513  3.7160  3.6477
-3.5513  3.7160  3.6477
[ CPUFloatType{2,3} ]
 0.3095  1.4035 -0.0349
 0.3095  1.4035 -0.0349
 0.3095  1.4035 -0.0349
 0.3095  1.4035 -0.0349
[ CPUFloatType{4,3} ]
 5.5000
 5.5000
[ CPUFloatType{2} ]