Removing bias toward positive direction of parameter space in amoeba …

…initialization
BIC-MNI · Feb 4, 2014 · 2166db5 · 2166db5
1 parent 3f3486f
commit 2166db5
Showing 1 changed file with 29 additions and 4 deletions.
diff --git a/minctracc/Optimize/amoeba.c b/minctracc/Optimize/amoeba.c
@@ -247,6 +247,11 @@ static  VIO_Real  get_function_value(
     VIO_Real              tolerance )
 {
     int    i, j;
+    float *parameter_fwd;
+    float *parameter_bwd;
+    VIO_Real cost_fwd;
+    VIO_Real cost_bwd;
+
 
     amoeba->n_parameters = n_parameters;
     amoeba->function = function;
@@ -257,6 +262,9 @@ static  VIO_Real  get_function_value(
     ALLOC( amoeba->values, n_parameters+1 );
 
     ALLOC( amoeba->sum, n_parameters );
+    ALLOC( parameter_fwd, n_parameters);
+    ALLOC( parameter_bwd, n_parameters);
+
 
     for(j=0; j<n_parameters; j++)
         amoeba->sum[j] = 0.0;
@@ -265,14 +273,31 @@ static  VIO_Real  get_function_value(
     {
         for(j=0; j<n_parameters; j++)
         {
-            amoeba->parameters[i][j] = (float) initial_parameters[j];
+            parameter_fwd[j] = (float) initial_parameters[j];
+            parameter_bwd[j] = (float) initial_parameters[j];
             if( i > 0 && j == i - 1 )
-                amoeba->parameters[i][j] += parameter_delta;
-            amoeba->sum[j] += amoeba->parameters[i][j];
+            {
+              parameter_fwd[j] += parameter_delta;
+              parameter_bwd[j] -= parameter_delta;
+            }
         }
+
+      // Test the parameters 
+      cost_fwd = get_function_value( amoeba, parameter_fwd);
+      cost_bwd = get_function_value( amoeba, parameter_bwd);
+
+      // Use the one with the lowest value
+      for(j=0; j<n_parameters; j++)
+      {
+          amoeba->parameters[i][j] = ( cost_fwd < cost_bwd ) ? parameter_fwd[j] : parameter_bwd[j];
+          amoeba->sum[j] += amoeba->parameters[i][j];
+      }
+      amoeba->values[i] = ( cost_fwd < cost_bwd ) ? cost_fwd : cost_bwd;
 
-        amoeba->values[i] = get_function_value( amoeba, amoeba->parameters[i] );
     }
+
+    FREE( parameter_fwd );
+    FREE( parameter_bwd );
 }
 
 /* ----------------------------- MNI Header -----------------------------------