As part of a larger solution, I've established that I've implemented something incorrectly regarding solving the system
$Uz=y$
Where U is the upper triangular submatrix resultant from an LU=A decomposition.
What I have is; (assuming zero based indexing)
$z_{n-1}=y_{n-1}/U_{n-1,n-1}$
$for\ i=n-2;i>=0;i--$
$\ \ t=0$
$\ \ for\ j=i+1; j
$\ \ \ \ t-=U_{i,j}y_j$
$\ \ z_i=(y_i-t)/=U_{i,i}$
This is coming from my reading of Goulb and Van Loan but I could be making a mistake.
In a nutshell, all the z values except for z[0] are correct.
Notes; the LU decomposition used is lower unitary i.e diag L are all 1,
For anyone interested in the larger problem be my guest, but as far as I can see this is the last thing wrong.
POST-ANSWER UPDATE: Finished the solver, thanks everyone for your help.