Address comments, add tolerance (idaholab#6389)

modules/phase_field/include/postprocessors/FindValueOnLine.h

@@ -17,7 +17,11 @@ template<>
 InputParameters validParams<FindValueOnLine>();
 
 /**
- * Finds a secific value along a line through a bisection search/
+ * Find a specific target value along a sampling line. The variable values along
+ * the line should change monotonically. The target value is searched using a
+ * bisection algorithm.
+ * The Postprocessor reports the distance from the start_point along the line
+ * between start_point and end_point.
  */
 class FindValueOnLine : public GeneralPostprocessor, public Coupleable
 {
@@ -45,6 +49,9 @@ class FindValueOnLine : public GeneralPostprocessor, public Coupleable
   /// search depth
   const unsigned int _depth;
 
+  /// tolerance for comparison to the target value
+  const Real _tol;
+
   /// coupled variable
   MooseVariable * _coupled_var;
 

modules/phase_field/src/postprocessors/FindValueOnLine.C

@@ -12,10 +12,12 @@ template<>
 InputParameters validParams<FindValueOnLine>()
 {
   InputParameters params = validParams<GeneralPostprocessor>();
-  params.addParam<Point>("start_point", "Start point of the sample line.");
-  params.addParam<Point>("end_point", "End point of the sample line.");
+  params.addClassDescription("Find a specific target value along a sampling line. The variable values along the line should change monotonically. The target value is searched using a bisection algorithm.");
+  params.addParam<Point>("start_point", "Start point of the sampling line.");
+  params.addParam<Point>("end_point", "End point of the sampling line.");
   params.addParam<Real>("target", "Target value to locate.");
-  params.addParam<unsigned int>("depth", "Number of bisections to perform.");
+  params.addParam<unsigned int>("depth", 30, "Maximum number of bisections to perform.");
+  params.addParam<Real>("tol", 1e-10, "Stop search if a value within a symmetric interval of this with around the target is found.");
   params.addCoupledVar("v", "Variable to inspect");
   return params;
 }
@@ -28,6 +30,7 @@ FindValueOnLine::FindValueOnLine(const InputParameters & parameters) :
     _length((_end_point - _start_point).norm()),
     _target(getParam<Real>("target")),
     _depth(getParam<unsigned int>("depth")),
+    _tol(getParam<Real>("tol") / 2.0),
     _coupled_var(getVar("v", 0)),
     _position(0.0),
     _mesh(_subproblem.mesh()),
@@ -60,6 +63,10 @@ FindValueOnLine::execute()
     // sample value
     Real value = getValueAtPoint(p);
 
+    // have we hit the target value yet?
+    if (value > _target - _tol && value < _target + _tol)
+      break;
+
     // bisect
     if (   (left >= _target && _target >= value)
         || (left <= _target && _target <= value))
@@ -103,7 +110,7 @@ FindValueOnLine::getValueAtPoint(const Point & p)
   else
   {
     // there is no element
-    mooseError("No element found.");
+    mooseError("No element found at the current search point. Please make sure the sampling line stays inside the mesh completely.");
   }
 }