Makes biasstep_rebias an action, and simple docs page

docs/index.rst

@@ -22,6 +22,7 @@ Contents
 
    operations/setup
    operations/bias_steps
+   operations/biasstep_rebias
    operations/iv
    operations/squid_curves
    operations/complex_impedance

docs/operations/biasstep_rebias.rst

@@ -0,0 +1,48 @@
+Bias Step Rebias
+================================
+
+For various reasons, it may be beneficial to bias or rebias detectors into their
+transition using bias-step functions instead of IVs, since
+- bias steps can be much faster than IVs
+- bias steps don't require overbiasing
+
+Yuhan Wang has developed the bias-step rebiasing function to find a suitable
+bias-point using just bias steps, which is described in greater detail in `his
+spie proceeding <https://arxiv.org/abs/2107.13504>`_.
+
+The general control flow is as follows:
+
+    1. Take initial bias steps bsa_0
+        will rebias if there are any bias lines where R0 is all nan
+        If >10% of dets are have Rfrac < 0.1, marks bg as overbias_needed
+        If >50% of dets have Rfrac > 0.9, marks bg as normal (and drop from normal needed)
+    2. Overbias overbias_needed bgs
+        runs overbias_dets on bgs that need overbiasing, and waits
+        For biaslines that have been overbiased, set the DC bias voltage to testbed_100mK_bias_voltage
+        Run bias steps
+            (no bias retry here)
+        Check normal condition (above) and add updated bias lines to bg_detectors_normal array if they meet it
+    3. Drop from normal
+        For each normal bg, step voltage by 0.5(V_norm - V_SC) determined from IV
+        Run bias steps
+            update bsa_0 so it's always the last bias step ran
+            These bias steps don't have a retry
+        Check normal condition. If any bgs are still normal, repeat.
+        After exiting loop, the resulting DC biases are initial_dc_biases
+    4. Find new bjas voltage and take bias steps:
+        vspread is diff between median normal and median SC voltages based on IV
+        New bias voltage is init +/- 0.15*vspread where +/- is determined by
+        whether or not the median Rfrac is > or < than 0.5
+        Take bias steps (bsa_1) and retry if needed
+    5. Determine new bias point for each channel:
+        v_estimate = (v0 (target - Rfrac_1) + v1 (Rfrac_0 - target)) / (Rfrac_0 - Rfrac_1)
+        vnew = median(v_estimate[bg]), or if all are nan, vnew = (v1 - v0) / 2
+    6. Set bias to vnew and retake bias steps bsa_2 (with retry if needed)
+        BG is successful if abs(Rfrac - target) < 0.05
+    7. Fine tuning unsuccessful bias groups
+        Step 0.15 vspread in the appropriate direction
+        Take bias steps (with retry)
+        v_estimate2 = (v0 (target - Rfrac_1) + v1 (Rfrac_0 - target)) / (Rfrac_0 - Rfrac_1)
+            with v0= prev estimate and v1 = prev estimate + delta
+        Apply v_estimate2, retake bias steps.
+    8. Return final bias step and bias voltages

sodetlib/operations/bias_dets.py

@@ -201,6 +201,7 @@ def bias_to_rfrac(S, cfg, rfrac=0.5, bias_groups=None, iva=None,
 
     return biases
 
+sdl.set_action()
 def biasstep_rebias(
         S, cfg, target_percentage_rn = 0.5, bias_groups=None,
         show_plots=True, make_plots=True):