[Cleanup] Rewrite state update

src/one-body-sample.cc

@@ -531,22 +531,24 @@ int main(int argc, char *argv[]) {
       // Q: is this reasonable?
       VectorType u;
       VectorType u_saved;
+      SingletonVectorType alpha_saved;
       double lastStateCorrection;
       for (size_t state_fpi = 1; state_fpi <= state_fpi_max; ++state_fpi) {
         stateUpdater->solve(v);
-        {
-          SingletonVectorType computed_state;
-          stateUpdater->extractState(computed_state);
-          double const stateCorrection =
-              stateEnergyNorm.diff(computed_state, alpha);
+        stateUpdater->extractState(alpha);
 
-          if (state_fpi <= 2 or stateCorrection <
-              requiredReduction * lastStateCorrection) {
-            alpha = computed_state;
+        if (state_fpi == 1)
+          relaxationWriter << "N ";
+        else {
+          double const stateCorrection =
+              stateEnergyNorm.diff(alpha, alpha_saved);
+          if (state_fpi <=
+              2 // lastStateCorrection is only set for state_fpi > 2
+              or stateCorrection < requiredReduction * lastStateCorrection)
             relaxationWriter << "N ";
-          } else {
-            alpha *= relaxation;
-            Arithmetic::addProduct(alpha, 1.0 - relaxation, computed_state);
+          else {
+            alpha *= (1.0 - relaxation);
+            Arithmetic::addProduct(alpha, relaxation, alpha_saved);
             relaxationWriter << "Y ";
           }
           lastStateCorrection = stateCorrection;
@@ -569,6 +571,7 @@ int main(int argc, char *argv[]) {
         if (state_fpi == state_fpi_max)
           DUNE_THROW(Dune::Exception, "FPI failed to converge");
 
+        alpha_saved = alpha;
         u_saved = u;
       }
       if (printProgress)