谁能帮我看下这个MATLAB代码，运行时为什么第4行LB未定义

function [x,fm] = IntProgFZ(f,A,b,Aeq,beq,lb,ub)
x = NaN;
fm = NaN;
NF_lb = zeros(size(lb));
NF_ub = zeros(size(ub));
NF_lb(:,1) = lb;
NF_ub(:,1) = ub;
F = inf;

while 1
sz = size(NF_lb);
k = sz(2);
opt = optimset('TolX',1e-9);
[xm,fv,exitflag] = linprog(f,A,b,Aeq,beq,NF_lb(:,1),NF_ub(:,1),[],opt);
if exitflag == -2
xm = NaN;
fv = NaN;
end
if xm == NaN
fv = inf;
end
if fv ~= inf
if fv < F
if max(abs(round(xm) - xm))<1.0e-7
F = fv;
x = xm;
tmpNF_lb = NF_lb(:,2:k);
tmpNF_ub = NF_ub(:,2:k);
NF_lb = tmpNF_lb;
NF_ub = tmpNF_ub;
if isempty(NF_lb) == 0
continue;
else
if x