Sheila, Chris, Stefan

In order to tackle the changing sensing matrix problem today we tried to use the soft-hard degree of freedoms. The theory
is that the beam overlap is much more sensitive to the hard DoF, thus this should be the one that is easily sensed independent
of the sensing-matrix-of-the-day. Then a gain hierarchy could be used to lock down everything.

Thus we started with calculation the theoretical hard-soft output matrix. Details can be found at
https://gwic.ligo.org/thesisprize/2011/dooley_thesis.pdf
For reference, the desin RoCs are ETM: 2245m, ITM: 1934m, giving (with L=3994.5m) g_ETM =-0.779, g_ITM =-1.065. 

We messed up the initial calculation and worked with
ITM =   .571  .495  * SOFT 
ETM    -.495  .571    HARD 
for yaw, and opposite off-diagonal sign for pitch.

while we should have used
ITM =   1.000 -0.867  * SOFT 
ETM     0.867  1.000   HARD 

We verified that the corresponding modes were mostly hard/soft by observing the power drop for a fixed offset in soft/hard.
The hard mode has the bigger power drop. 


Next we engaged DoF's one at a time, starting with the hard modes.

For yaw, DoF2 (hard mode) we inverted the last measured sensing matrix and converted it into the soft/hard basis. We got
SOFT =   5.14  11.7 *  WFS A 
HARD    -.272  1.04    WFS B
The hard loop easily closed that way. 

For the pitch DoF's we first tried the same scheme, but noticed that the hard mode ended up much stronger in what should have
been the soft signal. So instead we used the diagonal matrix WFS A -> hard, WFS B -> soft
SOFT =   0 1 *  WFS A 
HARD     1 0    WFS B
Again closing that loop was straight forward.

Next we closed the soft loops with low gain. That seemed straight forward. But then we started noticing that we saturated the PUM
with slow signals because the top-mass bleed-off was too slow. (We moved the bleed-off filters to the unused UIM filters to keep
the reliev script working.)

Before we could fix the saturation issue we noticed that the cavity transmitted spot on the camera did no longer line up
with the straight shot beam once all loops were on. So we manually realigned the cavity and tried to reengage the WFS, loop-by-loop.
Yaw hard worked fine, but to our surprise pitch hard didn't work at all - the error signal behaviour was completely different.

So our tentative conclusion is that our "sensing matrix of the day" doesn't seem provide a clean signal for the supposedly easy
hard pitch mode.