Linking issue to nmatrix.so

[lschneiderbauer]

When compiling the library with
bundle exec rake compile
I get some linker errors:

cd tmp/x86_64-linux/spice_rub/2.4.5
/usr/bin/gmake
compiling ../../../../ext/spice_rub/spice_ephemerides.c
compiling ../../../../ext/spice_rub/spice_geometry.c
compiling ../../../../ext/spice_rub/spice_kernel.c
compiling ../../../../ext/spice_rub/spice_rub.c
compiling ../../../../ext/spice_rub/spice_time.c
linking shared-object spice_rub.so
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: spice_ephemerides.o: in function sr_spkpos': spice_ephemerides.c:(.text+0xce): undefined reference to rb_nmatrix_dense_create'
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: spice_ephemerides.o: in function sr_spkezr': spice_ephemerides.c:(.text+0x1ee): undefined reference to rb_nmatrix_dense_create'
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: spice_ephemerides.o: in function sr_pxform': spice_ephemerides.c:(.text+0x2e1): undefined reference to rb_nmatrix_dense_create'
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: spice_ephemerides.o: in function sr_pxfrm2': spice_ephemerides.c:(.text+0x3c8): undefined reference to rb_nmatrix_dense_create'
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: spice_ephemerides.o: in function sr_sxform': spice_ephemerides.c:(.text+0x497): undefined reference to rb_nmatrix_dense_create'
/usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: spice_ephemerides.o:spice_ephemerides.c:(.text+0x605): more undefined references to rb_nmatrix_dense_create' follow collect2: error: ld returned 1 exit status gmake: *** [Makefile:259: spice_rub.so] Error 1 rake aborted! Command failed with status (2): [/usr/bin/gmake...] /home/lukas/.gem/ruby/2.4.0/gems/rake-compiler-0.9.9/lib/rake/extensiontask.rb:157:in block (2 levels) in define_compile_tasks'
/home/lukas/.gem/ruby/2.4.0/gems/rake-compiler-0.9.9/lib/rake/extensiontask.rb:156:in `block in define_compile_tasks'
Tasks: TOP => compile => compile:x86_64-linux => compile:spice_rub:x86_64-linux => copy:spice_rub:x86_64-linux:2.4.5 => tmp/x86_64-linux/spice_rub/2.4.5/spice_rub.so
(See full trace by running task with --trace)

The nmatrix package was installed before by executing bundle install.
I tried to manipulate the Makefile to directly include the nmatrix.so path, so that the linking could be completed. But then when requiring the spice_rub module in ruby-code it fails by complaining again that it cannot find nmatrix.so.

What is the solution to this?