function is_external = mtt_is_external (comp_type,outsig, insigs, is_port)
## usage: is_external = mtt_is_external (comp_type,outsig, insigs, is_port)
##
## This is to determine if mtt_component_equation should look for
## another equation. If is_external, the varable is available as a
## system input and therfore requires no further equation.
## I suspect that it needs more work.
if nargin<4
is_port = 0;
endif
is_external = 0; # Default
if is_port
is_external = 0;
elseif strcmp(comp_type,"SS");
is_external = insigs(1,2)!=outsig(2);
else
is_external = 0;
endif
endfunction