STYLE: Remove sigma4factor from StochasticGradientDescent Optimizers

The local variable `sigma4factor` has been equal to `1.0` for more than 16 years. (Starting with commit a90c96a, 16 Jan 2008).

Author: N-Dekker

Components/Optimizers/AdaptiveStochasticGradientDescent/elxAdaptiveStochasticGradientDescent.hxx

@@ -575,13 +575,12 @@ AdaptiveStochasticGradientDescent<TElastix>::AutomaticParameterEstimationOrigina
   }
 
   /** Measure square magnitude of exact gradient and approximation error. */
-  const double sigma4factor = 1.0;
-  double       sigma4 = 0.0;
-  double       gg = 0.0;
-  double       ee = 0.0;
+  double sigma4 = 0.0;
+  double gg = 0.0;
+  double ee = 0.0;
   if (maxJJ > 1e-14)
   {
-    sigma4 = sigma4factor * delta / std::sqrt(maxJJ);
+    sigma4 = delta / std::sqrt(maxJJ);
   }
   this->SampleGradients(this->GetScaledCurrentPosition(), sigma4, gg, ee);
   timer3.Stop();
@@ -709,7 +708,6 @@ AdaptiveStochasticGradientDescent<TElastix>::AutomaticParameterEstimationUsingDi
     double sigma4 = 0.0;
     double gg = 0.0;
     double ee = 0.0;
-    double sigma4factor = 1.0;
 
     /** Sample the grid and random sampler container to estimate the noise factor. */
     if (this->m_NumberOfGradientMeasurements == 0)
@@ -722,7 +720,7 @@ AdaptiveStochasticGradientDescent<TElastix>::AutomaticParameterEstimationUsingDi
     timer5.Start();
     if (maxJJ > 1e-14)
     {
-      sigma4 = sigma4factor * delta / std::sqrt(maxJJ);
+      sigma4 = delta / std::sqrt(maxJJ);
     }
     this->SampleGradients(this->GetScaledCurrentPosition(), sigma4, gg, ee);
 

Components/Optimizers/PreconditionedStochasticGradientDescent/elxPreconditionedStochasticGradientDescent.hxx

@@ -637,12 +637,11 @@ PreconditionedStochasticGradientDescent<TElastix>::AutomaticPreconditionerEstima
   /** Sample the fixed image to estimate the noise factor. */
   itk::TimeProbe timer_noise;
   timer_noise.Start();
-  double sigma4factor = 1.0;
   double sigma4 = 0.0;
   log::info(std::ostringstream{} << "  The estimated MaxJJ is: " << maxJJ);
   if (maxJJ > 1e-14)
   {
-    sigma4 = sigma4factor * this->m_MaximumStepLength / std::sqrt(maxJJ);
+    sigma4 = this->m_MaximumStepLength / std::sqrt(maxJJ);
   }
   double gg = 0.0;
   double ee = 0.0;