Possible MacOSX visualization crash

[teopb]

When trying to run ode_demo.py with --viz on macosx I am getting the following crash.

(pytorch) ➜  examples git:(master) python ode_demo.py --viz
2019-04-28 12:17:30.404 python[23732:2807027] -[NSApplication _setup:]: unrecognized selector sent to instance 0x7ffb17c3fd10
2019-04-28 12:17:30.406 python[23732:2807027] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSApplication _setup:]: unrecognized selector sent to instance 0x7ffb17c3fd10'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff4f8cf68b __exceptionPreprocess + 171
	1   libobjc.A.dylib                     0x00007fff76b60c76 objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff4f9681e4 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
	3   CoreFoundation                      0x00007fff4f845b50 ___forwarding___ + 1456
	4   CoreFoundation                      0x00007fff4f845518 _CF_forwarding_prep_0 + 120
	5   libtk8.6.dylib                      0x0000000121a2e31d TkpInit + 413
	6   libtk8.6.dylib                      0x000000012198617e Initialize + 2622
	7   _tkinter.cpython-37m-darwin.so      0x000000011dfe7a0f _tkinter_create + 1183
	8   python                              0x0000000108639116 _PyMethodDef_RawFastCallKeywords + 230
	9   python                              0x0000000108775e42 call_function + 306
	10  python                              0x0000000108773aec _PyEval_EvalFrameDefault + 46092
	11  python                              0x000000010876749e _PyEval_EvalCodeWithName + 414
	12  python                              0x0000000108637de7 _PyFunction_FastCallDict + 231
	13  python                              0x00000001086ba381 slot_tp_init + 193
	14  python                              0x00000001086c4361 type_call + 241
	15  python                              0x0000000108638ae3 _PyObject_FastCallKeywords + 179
	16  python                              0x0000000108775ed5 call_function + 453
	17  python                              0x0000000108773be0 _PyEval_EvalFrameDefault + 46336
	18  python                              0x00000001086388d5 function_code_fastcall + 117
	19  python                              0x0000000108775dc7 call_function + 183
	20  python                              0x0000000108773aec _PyEval_EvalFrameDefault + 46092
	21  python                              0x000000010876749e _PyEval_EvalCodeWithName + 414
	22  python                              0x0000000108637de7 _PyFunction_FastCallDict + 231
	23  python                              0x000000010863bce2 method_call + 130
	24  python                              0x0000000108639752 PyObject_Call + 130
	25  python                              0x0000000108773d58 _PyEval_EvalFrameDefault + 46712
	26  python                              0x000000010876749e _PyEval_EvalCodeWithName + 414
	27  python                              0x0000000108638fe3 _PyFunction_FastCallKeywords + 195
	28  python                              0x0000000108775dc7 call_function + 183
	29  python                              0x0000000108773be0 _PyEval_EvalFrameDefault + 46336
	30  python                              0x000000010876749e _PyEval_EvalCodeWithName + 414
	31  python                              0x00000001087ca9a0 PyRun_FileExFlags + 256
	32  python                              0x00000001087c9e17 PyRun_SimpleFileExFlags + 391
	33  python                              0x00000001087f7d3f pymain_main + 9663
	34  python                              0x000000010860b66d main + 125
	35  libdyld.dylib                       0x00007fff7777a015 start + 1
	36  ???                                 0x0000000000000003 0x0 + 3

Following advice here I inserted the following above if args.viz at aprox ln 57

from sys import platform as sys_pf
if sys_pf == 'darwin':
    import matplotlib
    matplotlib.use("TkAgg")

And it ran fine.