}// SBTree (constructor)
/// <summary>Initialize the root node and its children.
/// </summary>
public void Reset()
{
root = new SBTnode(null);
root._p = root._q = 1;
Grow(root);
}// Reset
}// Grow
/// <summary>Return node to the left.
/// </summary>
/// <param name="node">An SBTnode.
/// </param>
/// <returns>Node to the left.
/// </returns>
private SBTnode Previous(SBTnode node)
{
Debug.Assert(node.parent != null);
while (node.parent.right != null && node.parent.right != node)
{
node = node.parent;
}
return(node.parent);
}// Previous
}// Previous
/// <summary>Return node to the right.
/// </summary>
/// <param name="node">An SBTnode.
/// </param>
/// <returns>Node to the right.
/// </returns>
private SBTnode Next(SBTnode node)
{
Debug.Assert(node.parent != null);
while (node.parent.left != null && node.parent.left != node)
{
node = node.parent;
}
return(node.parent);
}// Next
}// Next
// The following function must return the numerator and
// denominator of the rational approximation.
/// <summary>Approximate a number with a given precision.
/// </summary>
/// <param name="x">Number to approximate.</param>
/// <param name="n">Precision in number of decimal places.
/// </param>
/// <returns>An instance of {Results}.
/// </returns>
public Results Approximate(double x, int n)
{
if (NotPositive(x))
{
MessageBox.Show(
String.Format("SBTree.Approximate: argument 'x' (== {0}) must be positive.",
x));
return(new Results(0, 1, x, 0.0, new List <Tuple <int, int, double> >()));
}
else
{
double epsilon = Math.Pow((double)10.0, (double)(-n));
double approx = (double)1.0;
List <Tuple <int, int, double> > sequence = new List <Tuple <int, int, double> >();
// Call {Reset} if this function is to be used repeatedly.
SBTnode current = root; // Starting point is the tree root.
do
{
// Record current approximation.
sequence.Add(new Tuple <int, int, double>(current._p, current._q, approx));
// Move left or right.
if (x > approx)
{
current = current.right;
}
else
{
current = current.left;
}
// Grow the children of {current} node.
Grow(current);
// Update the approximation.
approx = (double)current._p / (double)current._q;
} while (Math.Abs(x - approx) > epsilon);
return(new Results(current._p, current._q, x, approx, sequence));
}
}// Approximate
}// Reset
/// <summary>Add left and right children to a node.
/// </summary>
/// <param name="node">Node to which the children will be added.
/// </param>
private void Grow(SBTnode node)
{
// Add left child.
SBTnode left = new SBTnode(node);
node.left = left;
if (node._p == 1) // Node on left tree boundary == 1 / (n + 1).
{
left._p = 1;
left._q = node._q + 1;
}
else // Node is mediant of parent and previous node.
{
SBTnode previous = Previous(node);
left._p = node._p + previous._p;
left._q = node._q + previous._q;
}
// Add right child.
SBTnode right = new SBTnode(node);
node.right = right;
if (node._q == 1) // Node on right tree boundary == (n + 1) / 1.
{
right._q = 1;
right._p = node._p + 1;
}
else // Node is mediant of parent and next node.
{
SBTnode next = Next(node);
right._p = node._p + next._p;
right._q = node._q + next._q;
}
}// Grow
public SBTnode(SBTnode _parent)
{
_p = _q = 0;
left = right = null;
parent = _parent;
} // SBTnode (constructor)
