1. rewrite qrsolv (COD, test on lin2)
2. More/Sorensen method for mu calculation
3. better condition estimate for svd
4. Revisit h_fvv = 0.01 vs 0.02 (originally 0.01)
5. fdfvv test currently disabled in test_fdf.c - on MacOS, the lmaccel/box3d/fdfvv test fails
6. Tikhonov regularization