Bugfix: Unexpected behavior in SerialRefine caused by quiet NaNs (#605)

* Change argmax to nanargmax

* Add test example

* Add nan warning

* Updating warning message handling, removing temporary example.

* Cleaning up trailing whitespace as suggested by pre-commit.

* Remove unused import

---------

Co-authored-by: misha <msinner@nrel.gov>
Co-authored-by: Rafael M Mudafort <rafael.mudafort@nrel.gov>

floris/tools/optimization/yaw_optimization/yaw_optimizer_sr.py

@@ -19,11 +19,13 @@
 import numpy as np
 import pandas as pd
 
+from floris.logging_manager import LoggerBase
+
 # from .yaw_optimizer_scipy import YawOptimizationScipy
 from .yaw_optimization_base import YawOptimization
 
 
-class YawOptimizationSR(YawOptimization):
+class YawOptimizationSR(YawOptimization, LoggerBase):
     def __init__(
         self,
         fi,
@@ -240,8 +242,17 @@ def optimize(self, print_progress=True):
                 # Evaluate grid of yaw angles, get farm powers and find optimal solutions
                 farm_powers = self._process_evaluation_grid()
 
+                # If farm powers contains any nans, then issue a warning
+                if np.any(np.isnan(farm_powers)):
+                    err_msg = (
+                        "NaNs found in farm powers during SerialRefine "
+                        "optimization routine. Proceeding to maximize over yaw "
+                        "settings that produce valid powers."
+                    )
+                    self.logger.warning(err_msg, stack_info=True)
+
                 # Find optimal solutions in new evaluation grid
-                args_opt = np.expand_dims(np.argmax(farm_powers, axis=0), axis=0)
+                args_opt = np.expand_dims(np.nanargmax(farm_powers, axis=0), axis=0)
                 farm_powers_opt_new = np.squeeze(
                     np.take_along_axis(farm_powers, args_opt, axis=0),
                     axis=0,