急急急！！！请教高斯消去法的matlab程序

以下是一个高斯列主元消去法的程序，请如何将其改为高斯全主元消去法？？？
function [amax,P,L,U,x]=gepp(A,n,b)
% GEPP amax is the n-dim vector the maxmum element of every step
% aa is the max element of A; x is the solution;
% P*L*U=A:
B=A; P=1:n; U=zeros(n); L=zeros(n);
amax(1)=max(max(abs(A)));
for k=1:n-1
[s1,s2]=max(abs(B(:,1)));
B([1,s2],:)=B([s2 1],:);
m=k+s2-1; P([k m])=P([m k]);
U([m k],:)=U([k m],:); L([m k],:)=L([k m],:);
piv=B(2:n-k+1,1)/B(1,1); u=B(1,2:n-k+1);
U(k,k:n)=B(1,:); L(k+1:n,k)=piv;
B(1,:)=[]; B(:,1)=[];
B=B-piv*u; amax(k+1)=max(max(abs(B)));
end
U(n,n)=B; L=L+eye(n);

% Permutation and forward elimination
y = zeros(n,1);
for k = 1:n
j = 1:k-1;
y(k) = b(P(k)) - L(k,j)*y(j);
end

% Back substitution
x = zeros(n,1);
for k = n:-1:1
j = k+1:n;
x(k) = (y(k) - U(k,j)*x(j))/U(k,k);
end