Nice, I was looking for the --args python trick, didn’t know it.
The output is:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffad893700 (LWP 17317)]
torch::autograd::GradBuffer::addGrad(unsigned long, std::shared_ptr<torch::autograd::Variable>&&) (
    this=this@entry=0x7fffad892c40, pos=pos@entry=0, 
    var=var@entry=<unknown type in /home/moses/anaconda3/lib/python3.6/site-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so, CU 0x6e92e4, DIE 0x6fcb24>) at torch/csrc/autograd/grad_buffer.cpp:17
17	torch/csrc/autograd/grad_buffer.cpp: No such file or directory.
(gdb) bt
#0  torch::autograd::GradBuffer::addGrad(unsigned long, std::shared_ptr<torch::autograd::Variable>&&) (
    this=this@entry=0x7fffad892c40, pos=pos@entry=0, 
    var=var@entry=<unknown type in /home/moses/anaconda3/lib/python3.6/site-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so, CU 0x6e92e4, DIE 0x6fcb24>) at torch/csrc/autograd/grad_buffer.cpp:17
#1  0x00007fffed45c9a1 in torch::autograd::Engine::evaluate_function (this=this@entry=0x7fffedcd7ce0 <engine>, 
    task=...) from /home/<user>/anaconda3/lib/python3.6/site-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so
#2  0x00007fffed45dd1a in torch::autograd::Engine::thread_main (this=this@entry=0x7fffedcd7ce0 <engine>, queue=...)
   from /home/<user>/anaconda3/lib/python3.6/site-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so
#3  0x00007fffed46e87a in PythonEngine::thread_main (this=0x7fffedcd7ce0 <engine>, queue=...)
   from /home/<user>/anaconda3/lib/python3.6/site-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so
#4  0x00007ffff652d870 in ?? () from /home/<user>/anaconda3/bin/../lib/libstdc++.so.6
#5  0x00007ffff7474184 in start_thread (arg=0x7fffad893700) at pthread_create.c:312
#6  0x00007ffff688cbed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
(gdb) 

thx for your help