private static PointD FindMostSignificant(Calculator calc, CalculatedLine line, double leftBound, double rightBound, Mode mode)
{
if (line.Expression.Type != ExpressionType.Linear)
{
throw new ArgumentException("The line must be a linear one.");
}
if (line.PointData.Count == 0)
{
throw new ArgumentException("The calculated line must contain at least one line segment.");
}
RoughSignificant roughMax = GetRoughSignificant(line, calc, leftBound, rightBound, mode);
return RefineSignificant(calc, line, roughMax, mode);
}
private static PointD[] CalculateLine(Calculator calc, CalculatedLine line, double end, ref double pos)
{
if (pos > end)
{
throw new ArgumentException("The current position is greater than the end.");
}
int i = 0;
var filled = new PointD[(int)Math.Round(Math.Abs(end - pos) / line.Increment)];
while (end - pos > 1E-10 || pos < end)
{
calc.GraphingArgumentValue = pos;
filled[i++] = new PointD(pos * line.XScale,
calc.Evaluate(((StandardExpression)line.Expression).Expression) * line.YScale);
pos += line.Increment;
}
return filled;
}
/// <summary>
/// Finds every point on the specified line where that line crosses the X axis.
/// </summary>
/// <param name="calc">The calculator used to evaluate the expression.</param>
/// <param name="line">The line to test for zeros.</param>
/// <returns>
/// A list of points where the specified line crosses the X axis. If the line does not
/// cross the X axis at any point, the list will be empty.
/// </returns>
/// <remarks><para>
/// The algorithm used to find the zeros of a line is similar to the binary search
/// algorithm.
/// </para><para>
/// First, each point on the line is iterated through. In each iteration, it checks if the
/// sign of the Y values of the current point and the last point on the line are different.
/// For example, if we are iterating through the line "5x + 5," once we iterate through the
/// point (-1.5, -2.5) and (-0.5, 2.5), we find that the Y values have changed from negative
/// to positive. Those two points are then stored for later use. We repeat this process until
/// we reach the end of the line.
/// </para><para>
/// After we store each place where the Y values change signs, the binary search begins.
/// In a single iteration, we first determine if the left point of the pair (the minimum)
/// begins in the negative or positive side of the X axis. If it begins in the negative, it
/// is said to be moving "upward." Otherwise, it is moving "downward." This is important
/// because it determines what values are set to the high and low values for the binary
/// search. One of two things then happen:
/// </para><para>
/// In the case of the line going upward, if the sign of the middle value is negative, then
/// the low value becomes the middle value for the next iteration. Otherwise, the high value
/// becomes the middle value.
/// </para><para>
/// In the case of the line going downward, if the sign of the middle value is positive, then
/// the low value becomes the middle value for the next iteration. Otherwise, the high value
/// becomes the middle value.
/// </para><para>
/// This continues until the middle values for two consecutive iterations are the same value.
/// Once this happens, the limits of the precision and accuracy of the datatype we are using
/// (64-bit floating point in this specific implementation's case) has been reached, and the
/// search stops. The final middle value is the X value of the zero.
/// </para></remarks>
public static List<PointD> FindZeros(Calculator calc, CalculatedLine line)
{
if (line.Expression.Type != ExpressionType.Linear)
{
throw new ArgumentException("The expression type must be Linear.");
}
// Each PointF array represents the two points where the
// sign changes from positive to negative or vice versa
var signChanges = from roughZero in line.PointData.SelectMany(FindRoughZero)
select new
{
LowerBound = roughZero[0].X / line.XScale,
UpperBound = roughZero[1].X / line.XScale,
InitialSign = roughZero[0].Y < 0 ? Sign.Negative : Sign.Positive
};
// Find the corresponding zero for each sign change
var zeros = from change in signChanges
select RefineZero(calc, (StandardExpression)line.Expression, change.LowerBound, change.UpperBound, change.InitialSign);
return zeros.ToList();
}
private static IList<IList<PointD>> GetCompleteLine(Calculator calc, CalculatedLine line)
{
var regions = new List<IList<PointD>>();
double xScale = line.XScale;
double yScale = line.YScale;
int segmentIndex = 1;
int projSegments = line.PointData.Count - 1;
double pos = line.Window.MinimumX;
if (Math.Abs(line.PointData[0][0].X / xScale - pos) > 1E-10)
{
// There is a void region between the left side of the window and the first segment
segmentIndex = 0;
projSegments++;
}
for (int i = 0; i < projSegments; i++)
{
PointD[] filled = CalculateLine(calc,
line,
line.PointData[segmentIndex][0].X / xScale,
ref pos);
regions.Add(filled);
regions.Add(line.PointData[segmentIndex]);
pos = line.PointData[segmentIndex++].Last().X / xScale + line.Increment;
}
IList<PointD> lastSegment = line.PointData.Last();
if (Math.Abs(line.Window.MaximumX - lastSegment.Last().X / xScale) > 1E-10)
{
// There is a void region between the last segment and the right side of the window
regions.Add(CalculateLine(calc, line, line.Window.MaximumX, ref pos));
}
return regions;
}
public static PointD FindMinimum(Calculator calc, CalculatedLine line, double leftBound, double rightBound)
{
return FindMostSignificant(calc, line, leftBound, rightBound, Mode.Minimum);
}
private static PointD RefineSignificant(Calculator calc, CalculatedLine line, RoughSignificant roughSig, Mode mode)
{
double lo = roughSig.Left.X / line.XScale;
double hi = roughSig.Right.X / line.XScale;
double mid = (lo + hi) / 2;
double lastMid = double.NaN;
var stdExpr = (StandardExpression)line.Expression;
Func<double, int> derivComparer = mode == Mode.Maximum ? _maxDerivComparer : _minDerivComparer;
double y;
while (lastMid != mid)
{
double deriv = DerivativeCalculator.CalculateDerivative(calc, stdExpr, mid, out y);
int result = derivComparer(deriv);
if (result == -1)
{
lo = mid;
}
else if (result == 1)
{
hi = mid;
}
else
{
// Unlikely, but possible
break;
}
lastMid = mid;
mid = (lo + hi) / 2;
}
mid = Math.Round(mid, DerivativeCalculator.DeltaXPrecision);
calc.GraphingArgumentValue = mid;
y = calc.Evaluate(stdExpr.Expression);
return new PointD(mid, y);
}
private static RoughSignificant GetRoughSignificant(CalculatedLine line, Calculator calc, double leftBound, double rightBound, Mode mode)
{
IList<IList<PointD>> segments = line.PointData.Count > 1 ? GetCompleteLine(calc, line) : line.PointData;
double scaledLeftBound = leftBound * line.XScale;
double scaledRightBound = rightBound * line.XScale;
Func<double, double, bool> comparer = mode == Mode.Maximum ? _maxValComparer : _minValComparer;
var significant = new PointD(0, mode == Mode.Maximum ? double.MinValue : double.MaxValue);
int signifSegment = -1, signifPoint = -1;
for (int i = 0; i < segments.Count; i++)
{
var segment = segments[i];
for (int j = 0; j < segment.Count; j++)
{
var point = segment[j];
if (comparer(significant.Y, point.Y) && point.X >= scaledLeftBound && point.X <= scaledRightBound)
{
significant = point;
signifSegment = i;
signifPoint = j;
}
}
}
if (signifSegment == -1 || signifPoint == -1)
{
throw new Exception("No significant value could be found.");
}
// Get the points to the left and right of the rough maximum
PointD left;
PointD right;
GetSurroundingPoints(segments, signifSegment, signifPoint, out left, out right);
return new RoughSignificant(left, right);
}
private static List<PointD[]> FindRoughIntersections(CalculatedLine line1, CalculatedLine line2)
{
if (line1.XScale != line2.XScale || line1.YScale != line2.YScale)
{
throw new ArgumentException("The X and Y scales of both lines must be equal.");
}
double xScale = line1.XScale;
double yScale = line1.YScale;
var intersections = new List<PointD[]>();
IList<LineSegment> line1Segments = FlattenLine(line1);
IList<LineSegment> line2Segments = FlattenLine(line2);
int line1Pos = 1, line2Pos = 1;
while (line1Pos < line1Segments.Count && line2Pos < line2Segments.Count)
{
LineSegment last1 = line1Segments[line1Pos - 1];
LineSegment last2 = line2Segments[line2Pos - 1];
LineSegment current1 = line1Segments[line1Pos];
LineSegment current2 = line2Segments[line2Pos];
// If either current points are Starts, then the last points are not
// immediately "behind" them, and can't be considered for intersections
if (current1.Type == SegmentType.Continuation && current2.Type == SegmentType.Continuation)
{
bool finished = false;
// As long as either line is ahead of each other, advance the line that is behind
// This prevents false intersections from asymptotes and other singularities
while (!finished && line1Pos < line1Segments.Count && line2Pos < line2Segments.Count &&
(current1.Point.X < current2.Point.X || current1.Point.X > current2.Point.X))
{
line1Pos = SynchronizeLinePosition(line1Pos,
line1Segments,
current2,
ref current1,
ref last1,
ref finished);
if (finished)
{
break;
}
line2Pos = SynchronizeLinePosition(line2Pos,
line2Segments,
current1,
ref current2,
ref last2,
ref finished);
}
bool oneOnTop = last1.Point.Y > last2.Point.Y;
if (finished)
{
break;
}
// Make sure neither of the points are the start of a line segment, because if they
// are, the point before either one won't be immediately behind the current point
if (current1.Type != SegmentType.Start && current2.Type != SegmentType.Start &&
(current1.Point.Y > current2.Point.Y) != oneOnTop)
{
// Store the intersection and the four points that make it
intersections.Add(new[]
{
last1.Point.ScaleDown(xScale, yScale),
current1.Point.ScaleDown(xScale, yScale),
last2.Point.ScaleDown(xScale, yScale),
current2.Point.ScaleDown(xScale, yScale),
});
}
}
line1Pos++;
line2Pos++;
}
return intersections;
}
private static List<LineSegment> FlattenLine(CalculatedLine line)
{
var flattened =
line.PointData.SelectMany(t => t.Select((t1, i) =>
new LineSegment
{
Point = t1,
Type = i == 0
? SegmentType.Start
: SegmentType.Continuation
}));
return flattened.ToList();
}