Check valid orbit before correcting

Author: lfarv

docs/p/notebooks/response_matrices.ipynb

@@ -550,7 +550,7 @@
      "name": "stderr",
      "output_type": "stream",
      "text": [
-      "/Users/laurent/dev/libraries/at/pyat/at/latticetools/response_matrix.py:579: AtWarning: No new excluded value\n",
+      "/Users/laurent/dev/libraries/at/pyat/at/latticetools/response_matrix.py:584: AtWarning: No new excluded value\n",
       "  warnings.warn(AtWarning(\"No new excluded value\"), stacklevel=1)\n"
      ]
     }
@@ -591,7 +591,7 @@
      "name": "stderr",
      "output_type": "stream",
      "text": [
-      "/Users/laurent/dev/libraries/at/pyat/at/latticetools/response_matrix.py:579: AtWarning: No new excluded value\n",
+      "/Users/laurent/dev/libraries/at/pyat/at/latticetools/response_matrix.py:584: AtWarning: No new excluded value\n",
       "  warnings.warn(AtWarning(\"No new excluded value\"), stacklevel=1)\n"
      ]
     }

pyat/at/latticetools/response_matrix.py

@@ -466,8 +466,13 @@ def correct(
         if apply:
             self.variables.get(ring=ring, initial=True)
         sumcorr = np.array([0.0])
-        for _ in range(niter):
+        for it in range(niter):
             obs.evaluate(ring, **self.eval_args)
+            err = obs.flat_deviations
+            if np.any(np.isnan(err)):
+                raise AtError(
+                    f"Step {it + 1}: Invalid observables, cannot compute correction"
+                )
             corr = self.get_correction(obs.flat_deviations, nvals=nvals)
             sumcorr = sumcorr + corr  # non-broadcastable sumcorr
             if apply:
@@ -787,7 +792,7 @@ def set_norm():
                 cavrefs,
                 "Frequency",
                 name="RF frequency",
-                delta=cavdelta if cavdelta else 4.0 * cavd,
+                delta=cavdelta if cavdelta else 2.0 * cavd,
             )
             variables.append(cavvar)