%  slvTriDiagSys.m
%
%  solve a tri-diagonal system 
%  Gaussian elimination without pivoting
%  d -- main diagonal 
%  a -- sub diagonal 
%  c -- super diagonal 
%  b -- right-hand side 
%  n -- size of linear system 
%
%  Jiangguo (James) Liu,  ColoState 
%  03/25/2008

function  x = slvTriDiagSys(a, b, c, d, n)

%  forward substitution

for i=1:n-1
   d(i+1) = d(i+1) - a(i)/d(i)*c(i);
   b(i+1) = b(i+1) - a(i)/d(i)*b(i);
end

%  backward substitution

x(n) = b(n)/d(n);
for i=n-1:-1:1
   x(i) = (b(i)-c(i)*x(i+1))/d(i);
end

return;