function [ok] = tridiag_solve_pcg_ok()
ok = true;
m = 1;
n = 50;
N = 40;
eps = 1e-5;
% case where uk = 0, qk = I, and ak is random
%rand('seed', 123);
a = rand(n, n, N);
r = randn(n * N, m);
c = zeros(n, n, N);
for k = 1 : N
ak = a(:, :, k);
b(:, :, k) = 5 * eye(n) + ak * ak';
c(:, :, k) = ak';
end
% ----------------------------------------
[e, flag, relres, iter] = ckbs_tridiag_solve_pcg(b, c, r);
% ----------------------------------------
%
check = ckbs_blktridiag_mul(b, c, e);
max(abs(check - r))
ok = ok & max(abs(check - r))/max(abs(r)) < eps;
return
end