back_band.m

various matlab programs to slove various problems

function [b] = back_band (U, q, b)
[n,n]=size(U);
for j=n:-1:1
   b (j) = b (j) / U (j,j);
   for i = max(1,j-q):j-1
      b(i)=b(i)-U(i,j)*b(j);
   end
end
return