MATLAB: Mex compilation – undefined reference to `main’

mex

I am trying to compile Matlab interface of NOMAD algorithm (https://www.gerad.ca/nomad/Project/Home.html) in Ubuntu 14.04 using gcc-4.7.3.
After executing compilation script provided by algorithm manufacturer I get the following error:
>> GERAD_NOMAD_build
------------------------------------------------
NOMAD MEX FILE BUILD --- GERAD VERSION 
Warning: Legacy MEX infrastructure is provided for compatibility; it will be removed in a future
version of MATLAB. For more information, consult the MEX release notes
http://www.mathworks.com/help/matlab/release-notes.html. 
> In GERAD_NOMAD_build (line 145) 
-> mexopts.sh sourced from directory (DIR = $PREF_DIR)
   FILE = /home/bkhusain/.matlab/R2015a/mexopts.sh
----------------------------------------------------------------
->    MATLAB                = /usr/local/MATLAB/R2015a
->    CC                    = gcc
->    CC flags:
         CFLAGS             = -ansi -D_GNU_SOURCE  -fexceptions -fPIC -fno-omit-frame-pointer -pthread -std=c99
         CDEBUGFLAGS        = -g
         COPTIMFLAGS        = -O -DNDEBUG
         CLIBS              = -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
         arguments          = 
->    CXX                   = g++
->    CXX flags:
         CXXFLAGS           = -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread
         CXXDEBUGFLAGS      = -g
         CXXOPTIMFLAGS      = -O -DNDEBUG
         CXXLIBS            = -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
         arguments          = 
->    FC                    = gfortran
->    FC flags:
         FFLAGS             = -fexceptions -fbackslash -fPIC -fno-omit-frame-pointer
         FDEBUGFLAGS        = -g
         FOPTIMFLAGS        = -O
         FLIBS              = -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
         arguments          = 
->    LD                    = g++
->    Link flags:
         LDFLAGS            =  -Wl,-rpath,'/../lib/' 
         LDDEBUGFLAGS       = -g
         LDOPTIMFLAGS       = -O
         LDEXTENSION        = .mexa64
         arguments          =  -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/
->    LDCXX                 = 
->    Link flags:
         LDCXXFLAGS         = 
         LDCXXDEBUGFLAGS    = 
         LDCXXOPTIMFLAGS    = 
         LDCXXEXTENSION     = 
         arguments          =  -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/
----------------------------------------------------------------
-> g++ -c  -I. -I/home/bkhusain/nomad.3.7.3/src/ -I/usr/local/MATLAB/R2015a/extern/include -I/usr/local/MATLAB/R2015a/simulink/include -DMATLAB_MEX_FILE -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread  -O -DNDEBUG  "nomadmex.cpp"
-> g++ -O  -Wl,-rpath,'/../lib/'  -o  "/home/bkhusain/nomad.3.7.3/bin//nomad.mexa64"  nomadmex.o  -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/ -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 1 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 2 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 3 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 4 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 5 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 6 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 7 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 8 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 9 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 10 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 11 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 12 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 13 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 14 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 15 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 16 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 17 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 18 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 19 has invalid symbol index 21
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_line): relocation 0 has invalid symbol index 2
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
      mex: link of ' "/home/bkhusain/nomad.3.7.3/bin//nomad.mexa64"' failed.
Error using GERAD_NOMAD_build (line 166)
Error Compiling NOMAD!
Unable to complete successfully.
The error is thrown after executing:
mex -v -largeArrayDims nomadmex.cpp LDFLAGS='$LDFLAGS -Wl,-rpath,''$ORIGIN/../lib/'' '  -I.  -I/home/bkhusain/nomad.3.7.3/src/ -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/ -output /home/bkhusain/nomad.3.7.3/bin//nomad.mexa64
I don't understand why linker is complaining about missing reference to 'main', since main function is not required for mex compilation.

Best Answer

The problem was solved by adding the directory of required *.so files to the path manually. In ~/.bashrc I added:
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/bkhusain/Documents/MATLAB/nomad.3.7.3/lib
export LD_LIBRARY_PATH
Also when calling mex I removed LDFLAGS:
mex -v -largeArrayDims nomadmex.cpp -I.  -I/home/bkhusain/nomad.3.7.3/src/ -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/ -output /home/bkhusain/nomad.3.7.3/bin//nomad.mexa64
Still I do not understand why linker was looking for main() function. I will try to investigate this based on answer Jan Simon's answer
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