Why is this library not found?

Hello,

I librarified gneural_network, patches pending at:
https://lists.gnu.org/archive/html/gneuralnetwork/2016-04/msg00015.html
In that patch library is called libgneural_network, locally I modified 
name to libgneural.

Next I installed gneural_network at /opt:

/opt/gneural/
├── bin
│   └── gneural_network
├── include
│   └── gneural
│       ├── activation.h
│       ├── binom.h
│       ├── defines.h
│       ├── error.h
│       ├── fact.h
│       ├── feedforward.h
│       ├── genetic_algorithm.h
│       ├── gradient_descent.h
│       ├── includes.h
│       ├── load.h
│       ├── msmco.h
│       ├── parser.h
│       ├── randomize.h
│       ├── random_search.h
│       ├── rnd.h
│       ├── save.h
│       ├── simulated_annealing.h
│       └── structures.h
└── lib
     ├── libgneural.a
     ├── libgneural.la
     ├── libgneural.so -> libgneural.so.0.0.0
     ├── libgneural.so.0 -> libgneural.so.0.0.0
     └── libgneural.so.0.0.0

I try to load that library with lt_dlopen:

#include <ltdl.h>
#include <stdio.h>

int
main (int argc, char** argv)
{
   lt_dlhandle handle;
   lt_dlinit ();
   handle = lt_dlopen ("libgneural");
   if (handle != NULL)
     {
       printf ("Loaded library\n");
       lt_dlclose (handle);
     }
   else
     {
       printf (lt_dlerror ());
       printf ("\n");
     }
   return 0;
}

This program fails with error message: file not found. What am I doing 
wrong? The command line is:
$ gcc -l ltdl -o dlopen dlopen.c
$ LD_LIBRARY_PATH=/opt/gneural/lib ./dlopen

Best regards
Aljosha Papsch

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