/// <summary>
/// Runs the one-against-one learning algorithm.
/// </summary>
///
/// <param name="computeError">
/// True to compute error after the training
/// process completes, false otherwise. Default is true.
/// </param>
/// <param name="token">
/// A <see cref="CancellationToken"/> which can be used
/// to request the cancellation of the learning algorithm
/// when it is being run in another thread.
/// </param>
///
/// <returns>
/// The sum of squares error rate for
/// the resulting support vector machine.
/// </returns>
///
public double Run(bool computeError, CancellationToken token)
{
if (configure == null)
{
var excp = new InvalidOperationException("Please specify the algorithm configuration function "
+ "by setting the Algorithm property for this class. Examples are available in the "
+ "documentation for Multiclass Support Vector Learning class (given in the help link).");
excp.HelpLink = "http://accord-framework.net/svn/docs/html/T_BestCS_MachineLearning_VectorMachines_MulticlassSupportVectorMachine.htm";
throw excp;
}
int classes = msvm.Classes;
int total = (classes * (classes - 1)) / 2;
int progress = 0;
var pairs = new Tuple <int, int> [total];
for (int i = 0, k = 0; i < classes; i++)
{
for (int j = 0; j < i; j++, k++)
{
pairs[k] = Tuple.Create(i, j);
}
}
msvm.Reset();
// Save exceptions but process all machines
var exceptions = new ConcurrentBag <Exception>();
// For each class i
Parallel.For(0, total, k =>
{
if (token.IsCancellationRequested)
{
return;
}
int i = pairs[k].Item1;
int j = pairs[k].Item2;
// We will start the binary sub-problem
var args = new SubproblemEventArgs(i, j);
OnSubproblemStarted(args);
// Retrieve the associated machine
KernelSupportVectorMachine machine = msvm[i, j];
// Retrieve the associated classes
int[] idx = outputs.Find(x => x == i || x == j);
double[][] subInputs = inputs.Submatrix(idx);
int[] subOutputs = outputs.Submatrix(idx);
// Transform it into a two-class problem
subOutputs.ApplyInPlace(x => x = (x == i) ? -1 : +1);
// Train the machine on the two-class problem.
var subproblem = configure(machine, subInputs, subOutputs, i, j);
var canCancel = (subproblem as ISupportCancellation);
try
{
if (canCancel != null)
{
canCancel.Run(false, token);
}
else
{
subproblem.Run(false);
}
}
catch (Exception ex)
{
exceptions.Add(ex);
}
// Update and report progress
args.Progress = Interlocked.Increment(ref progress);
args.Maximum = total;
OnSubproblemFinished(args);
});
if (exceptions.Count > 0)
{
throw new AggregateException("One or more exceptions were thrown when teaching "
+ "the machines. Please check the InnerException property of this AggregateException "
+ "to discover what exactly caused this error.", exceptions);
}
// Compute error if required.
return((computeError) ? ComputeError(inputs, outputs) : 0.0);
}
