function niso = Visohhred(vv, iext);% VISOHHRED - computes n(V) for the dV/dt=0 isocline for the reduced (2 variable) HH% model. Uses fdvdt103 to evaluate dV/dt. iext must be a scalar. vv can be% a vector. returns niso with same size as vv. niso=NaN where there is no% solution.% NOTE: sethhparms must be called to set params of hh model before this is% used (see fdvdt103()).nvrange = 0.3;for jv=1:length(vv)    if fdvdt103(0, vv(jv), iext)*fdvdt103(1, vv(jv), iext)>=0        niso(jv) = NaN;      % There is no solution here, return NaN    else        [niso(jv),fval,exitflag] = fzero('fdvdt103', nvrange, [], vv(jv), iext);        if exitflag<0;            niso(jv) = NaN;  % Shouldn't happen, but one can never tell        end    endendreturn