Error of undeclared identifier while calling c-function in VHDL with ncsim

I am getting error of undeclared identifier while calling c-function in VHDL with ncsim.

I am trying to call C-functions existing in a .so filed - c_api.so inside a VHDL file, something like:

begin
    wait for 1 ns;
    if ( RESETEN = '1') then
       c_matrix_multi( size, cofficient_m1, cofficient_m2, cofficient_reduced);
    end if;
    wait;
end process initial;  

But i am getting following error of c-function name "c_matrix_multi" not declared.
                                c_matrix_multi( size, cofficient_m1, cofficient_m2, cofficient_reduced);
ncvhdl_p: *E,IDENTU (.../compute_cofficient.vhd,107|46): identifier (c_matrix_multi) is not declared [10.3].

Plz, provide a sample code of c-function being used inside VHDL using three steps (compile, elab and run).