%
% lookup_species
%
%   note: external species are indicated as negative values
function index = lookup_species(species_name)

global species_names;
global external_species_names;

if (strncmp(species_name, '*external*', 10) == 1)
    % treat external species using a negative index
    for i=1:size(external_species_names,2)
        if (strcmp(species_name, external_species_names{i}))
            index = -i;
            disp(['External ' species_name ', index ' num2str(index)]);
            return;
        end
    end
    external_species_names{size(external_species_names,2)+1} = species_name;
    index = -size(external_species_names,2);
    disp(['New external ' species_name ', index ' num2str(index)]);
else
    % internal species
    for i=1:size(species_names,2)
        if (strcmp(species_name, species_names{i}))
            index = i;
            return;
        end
    end

    species_names{size(species_names,2)+1} = species_name;
    index = size(species_names,2);
end

end