I have been having some difficulty successfully using external libraries in
a custom OOT module that I have not been able to understand.

I have had this issue with a few different external libraries.  The symptom
is a segmentation fault when a function in the external library is called.
The below example is just representative and a bit circular as we are going
from python->c++->python.

For this example, I would like to use matplotlib within a C++ OOT module to
visualize some data during the debug of my module.  I understand that this
is not something I would want to do within a gnu radio module during normal
usage and that there are other ways to visualize the data.

I am using matplotlib.cpp (https://github.com/lava/matplotlib-cpp) for this
purpose.  This is simply a header file that requires linking to the python
libraries.

To do this I have:

1. Included matplotlibcpp.h in my /lib folder.

2. In /lib/CMakeList.txt I have added the following:

find_package(PythonLibs 2.7)
include_directories(${Boost_INCLUDE_DIR} ${PYTHON_INCLUDE_DIRS} )
link_directories(${Boost_LIBRARY_DIRS}  ${PYTHON_LIBRARIES} )
...
target_link_libraries( gnuradio-mymodule   ${Boost_LIBRARIES}
${GNURADIO_ALL_LIBRARIES} ${PYTHON_LIBRARIES})


3. Within my general_work function I have added the following (as a test
only):

#include <cmath>
#include "matplotlibcpp.h"
namespace plt = matplotlibcpp;
...
general_work(...
...
      // This just creates an interesting figure to plot.
      int n = 5000;
      std::vector<double> x(n), y(n), z(n), w(n,2);
      for(int i=0; i<n; ++i) {
              x.at(i) = i*i;
              y.at(i) = sin(2*M_PI*i/360.0);
              z.at(i) = log(i);
      }

      plt::plot(x, y);
      plt::show();
...

I am able to build successfully but when I run my qa_XYZ.py unit test I get
a segmentation fault at the plt::plot(x,y) line.  removing these two plt::
lines results in no segmentation fault.  I have seen this same behavior
when linking with other (not python) libraries for different reasons so I
am suspecting that there is some fundamental issue with how I am
configuring CMakeLists.txt or what I am trying to do is not possible for
some other reason.

----
The following code runs without any issues on the same machine outside of
gnuradio.
--------------------------------------------------
#include <cmath>
#include "matplotlibcpp.h"

namespace plt = matplotlibcpp;

int main()
{
// Prepare data.
int n = 5000;
std::vector<double> x(n), y(n), z(n), w(n,2);
for(int i=0; i<n; ++i) {
x.at(i) = i*i;
y.at(i) = sin(2*M_PI*i/360.0);
z.at(i) = log(i);
}

plt::plot(x, y);
plt::show();
}
--------------------------------------------------
>g++ test.cpp -I/usr/include/python2.7 -lpython2.7

Any help would be appreciated.
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