function [X] = GECP (A, b)

n = length(A);

xnr = (1:n)';
for i = 1: n-1
  p = s = i;
  for k = i: n
    for l = i: n
      if A(k, l) > A(s, p)
        s = k;
        p = l;
      end
    end
  end
  %zamiana wierszy
  pom = A(i, :);
  A(i, :) = A(s, :);
  A (s, :) = pom;
  pom = b(i);
  b(i) = b(s);
  b(s) = pom;
  %zamaina kolumn
  pom = A(:, i);
  A(:, i) = A(:, p);
  A(:, p) = pom;
  pom = xnr(i);
  xnr(i) = xnr(p);
  xnr(p) = pom;
  A
  b

  for j = i+1:n
    k = A(j, i)./A(i, i);
    A(j, : ) = A(j, :) - k.*A(i, :)
    b(j) = b(j) - k.*b(i);
  end
end

X = b;

X(n) = b(n)./A(n,n);
for j=(n-1):-1:1
  for i=n:-1:j+1
    X(j) = X(j) - X(i).*A(j, i);
  end
  X(j) = X(j)./A(j, j);
 end
X(xnr) = X;
endfunction



function [X] = GEPP (A, b)

n = length(A);


for i = 1: n-1
  s = i;
  for k = i: n
    if abs(A(k, i)) > (A(s, i))
      s = k;
    end
  end
  A([s, i], :) = A([i, s], :);
  b([s, i]) = b([i,s]);

  for j = i+1:n
    k = A(j, i)./A(i, i);
    A(j, : ) = A(j, :) - k.*A(i, :)
    b(j) = b(j) - k.*b(i);
  end
end

X = b;
for j=n:-1:1
  for i=n:-1:j+1
    X(j) = X(j) - X(i).*A(j, i);
  end
  X(j) = X(j)./A(j, j);
 end

endfunction