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public static Slice ( Matrix m, IEnumerable |
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| m | Matrix | Input Matrix. |
| indices | IEnumerable |
The indices. |
| return | Matrix | |
public override IModel Generate(Matrix x, Vector y)
{
int N = y.Length;
Vector a = Vector.Zeros(N);
// compute kernel
Matrix K = Kernel.Compute(x);
int n = 1;
// hopefully enough to converge right? ;)
// need to be smarter about storing SPD kernels...
bool found_error = true;
while (n < 500 && found_error)
{
found_error = false;
for (int i = 0; i < N; i++)
{
found_error = y[i] * a.Dot(K[i]) <= 0;
if (found_error) a[i] += y[i];
}
n++;
}
// anything that *matters*
// i.e. support vectors
var indices = a.Indices(d => d != 0);
// slice up examples to contain
// only support vectors
return new KernelPerceptronModel
{
Kernel = Kernel,
A = a.Slice(indices),
Y = y.Slice(indices),
X = x.Slice(indices)
};
}
/// <summary>Builds a tree.</summary>
/// <param name="x">The Matrix to process.</param>
/// <param name="y">The Vector to process.</param>
/// <param name="depth">The depth.</param>
/// <param name="used">The used.</param>
/// <returns>A Node.</returns>
private Node BuildTree(Matrix x, Vector y, int depth, List<int> used, Tree tree)
{
if (depth < 0)
return BuildLeafNode(y.Mode());
var tuple = GetBestSplit(x, y, used);
var col = tuple.Item1;
var gain = tuple.Item2;
var measure = tuple.Item3;
// uh oh, need to return something?
// a weird node of some sort...
// but just in case...
if (col == -1)
return BuildLeafNode(y.Mode());
used.Add(col);
Node node = new Node
{
Column = col,
Gain = gain,
IsLeaf = false,
Name = Descriptor.ColumnAt(col)
};
// populate edges
List<Edge> edges = new List<Edge>(measure.Segments.Length);
for (int i = 0; i < measure.Segments.Length; i++)
{
// working set
var segment = measure.Segments[i];
var edge = new Edge()
{
ParentId = node.Id,
Discrete = measure.Discrete,
Min = segment.Min,
Max = segment.Max
};
IEnumerable<int> slice;
if (edge.Discrete)
{
// get discrete label
edge.Label = Descriptor.At(col).Convert(segment.Min).ToString();
// do value check for matrix slicing
slice = x.Indices(v => v[col] == segment.Min);
}
else
{
// get range label
edge.Label = string.Format("{0} <= x < {1}", segment.Min, segment.Max);
// do range check for matrix slicing
slice = x.Indices(v => v[col] >= segment.Min && v[col] < segment.Max);
}
// something to look at?
// if this number is 0 then this edge
// leads to a dead end - the edge will
// not be built
if (slice.Count() > 0)
{
Vector ySlice = y.Slice(slice);
// only one answer, set leaf
if (ySlice.Distinct().Count() == 1)
{
var child = BuildLeafNode(ySlice[0]);
tree.AddVertex(child);
edge.ChildId = child.Id;
}
// otherwise continue to build tree
else
{
var child = BuildTree(x.Slice(slice), ySlice, depth - 1, used, tree);
tree.AddVertex(child);
edge.ChildId = child.Id;
}
edges.Add(edge);
}
}
// problem, need to convert
// parent to terminal node
// with mode
if (edges.Count <= 1)
{
var val = y.Mode();
node.IsLeaf = true;
node.Value = val;
}
tree.AddVertex(node);
if(edges.Count > 1)
foreach (var e in edges)
tree.AddEdge(e);
return node;
}
private static LearningModel GenerateModel(IGenerator generator, Matrix x, Vector y, IEnumerable<object> examples, double trainingPct)
{
var descriptor = generator.Descriptor;
var total = examples.Count();
var trainingCount = (int)System.Math.Floor(total * trainingPct);
// 100 - trainingPercentage for testing
var testingSlice = GetTestPoints(total - trainingCount, total).ToArray();
// trainingPercentage for training
var trainingSlice = GetTrainingPoints(testingSlice, total).ToArray();
// training
var x_t = x.Slice(trainingSlice);
var y_t = y.Slice(trainingSlice);
// generate model
var model = generator.Generate(x_t, y_t);
model.Descriptor = descriptor;
// testing
object[] test = GetTestExamples(testingSlice, examples);
double accuracy = 0;
for (int j = 0; j < test.Length; j++)
{
// items under test
object o = test[j];
// get truth
var truth = Ject.Get(o, descriptor.Label.Name);
// if truth is a string, sanitize
if (descriptor.Label.Type == typeof(string))
truth = StringHelpers.Sanitize(truth.ToString());
// make prediction
var features = descriptor.Convert(o, false).ToVector();
var p = model.Predict(features);
var pred = descriptor.Label.Convert(p);
// assess accuracy
if (truth.Equals(pred))
accuracy += 1;
}
// get percentage correct
accuracy /= test.Length;
return new LearningModel { Generator = generator, Model = model, Accuracy = accuracy };
}
/// <summary>Generates.</summary>
/// <param name="X">The Matrix to process.</param>
/// <param name="k">The int to process.</param>
public void Generate(Matrix X, int k)
{
int n = X.Rows;
int d = X.Cols;
/***********************
* initialize parameters
***********************/
// convergence params
var log_probability = 0d;
var probability_difference = double.MaxValue;
var mu_difference = double.MaxValue;
// initialize centers with KMeans
KMeans kmeans = new KMeans();
var asgn = kmeans.Generate(X, k, new EuclidianDistance());
// tentative centers
var mu_k = kmeans.Centers;
// initial covariances (stored as diag(cov) 1 of k)
var sg_k = new Matrix(k, d);
for (int i = 0; i < k; i++)
{
var indices = asgn.Select((a, b) => new Tuple<int, int>(a, b)).Where(t => t.Item1 == i).Select(t => t.Item2);
var matrix = X.Slice(indices, VectorType.Row);
sg_k[i] = matrix.CovarianceDiag();
}
// mixing coefficient
var pi_k = asgn
.OrderBy(i => i)
.GroupBy(j => j)
.Select(g => (double)g.Count() / (double)asgn.Length)
.ToVector();
int max_iter = 100;
do
{
/***********************
* Expectation Step
***********************/
// responsibilty matrix: how much is gaussian k responsible for this point x
var z_nk = new Matrix(n, k);
for (int i = 0; i < n; i++)
{
// pi_j * N(x_n | mu_j, sigma_j)
for (int j = 0; j < k; j++)
z_nk[i, j] = pi_k[j] * Normal(X[i], mu_k[j], sg_k[j]);
var dn = z_nk[i].Sum();
if(dn == 0)
Console.WriteLine("Uh oh....");
z_nk[i].Each(z => z / dn);
}
/***********************
* Maximization Step
***********************/
var N_k = z_nk.Sum(VectorType.Row);
var mu_k_new = new Matrix(mu_k.Rows, mu_k.Cols);
for (int i = 0; i < k; i++)
{
var sum = Vector.Zeros(d);
for (int j = 0; j < n; j++)
sum += z_nk[j, i] * X[j];
mu_k_new[i] = sum / N_k[i];
}
var sg_k_new = new Matrix(k, d);
for (int i = 0; i < k; i++)
{
var sum = Vector.Zeros(d);
for (int j = 0; j < n; j++)
sum += z_nk[j, i] * (X[j] - mu_k_new[i]).Each(s => s * s);
sg_k_new[i] = sum / N_k[i];
}
var pi_k_new = N_k / n;
/***********************
* Convergence Check
***********************/
var new_log_prob = 0d;
for (int i = 0; i < n; i++)
{
var acc = 0d;
// pi_j * N(x_n | mu_j, sigma_j)
for (int j = 0; j < k; j++)
acc += pi_k[j] * Normal(X[i], mu_k[j], sg_k[j]);
new_log_prob += System.Math.Log(acc, System.Math.E);
}
// log likelihood differences
probability_difference = System.Math.Abs(log_probability - new_log_prob);
Console.WriteLine("Log Likelihoods (Total Points: {0}, k={1}, d={2})\nO: {3}\nN: {4}\nDifference: {5}\n", n, k, d, log_probability, new_log_prob, probability_difference);
log_probability = new_log_prob;
// centers differences
mu_difference = mu_k.GetRows()
.Zip(mu_k_new.GetRows(), (v1, v2) => new { V1 = v1, V2 = v2 })
.Sum(a => (a.V1 - a.V2).Norm());
Console.WriteLine("Centers:\nO: {0}\nN: {1}\nDifference: {2}\n", mu_k, mu_k_new, mu_difference);
mu_k = mu_k_new;
// covariance differences
double diff = sg_k.GetRows()
.Zip(sg_k_new.GetRows(), (v1, v2) => new { V1 = v1, V2 = v2 })
.Sum(a => (a.V1 - a.V2).Norm());
Console.WriteLine("Covariance:\nO: {0}\nN: {1}\nDifference: {2}\n", sg_k, sg_k_new, diff);
sg_k = sg_k_new;
// mixing differences
diff = (pi_k - pi_k_new).Each(s => System.Math.Abs(s)).Sum();
Console.WriteLine("Mixing Coeffs:\nO: {0}\nN: {1}\nDifference: {2}\n", pi_k, pi_k_new, diff);
pi_k = pi_k_new;
Console.WriteLine("-------------------------------------------------------------");
} while (probability_difference > .0000000001 && mu_difference > .0000000001 && --max_iter >= 0);
}
/// <summary>Generates a SVM model based on a set of examples.</summary>
/// <param name="X">The Matrix to process.</param>
/// <param name="y">The Vector to process.</param>
/// <returns>Model.</returns>
public override IModel Generate(Matrix X, Vector y)
{
this.Preprocess(X);
// expect truth = 1 and false = -1
y = y.ToBinary(k => k == 1d, falseValue: -1.0);
// initialise variables
int m = X.Rows, n = X.Cols, i = -1, j = -1, changes = 0, iterations = 0;
double lagLow = 0.0, lagHigh = 0.0, cost = 0.0, tempAI = 0d, tempAJ = 0d;
Vector gradient = Vector.Zeros(m), alpha = Vector.Zeros(m);
// precompute kernal matrix (using similarity function)
Matrix K = this.KernelFunction.Compute(X);
// synchronise SVM parameters with working set selection function.
this.SelectionFunction.Bias = this.Bias; this.SelectionFunction.C = this.C; this.SelectionFunction.Epsilon = this.Epsilon;
this.SelectionFunction.K = K; this.SelectionFunction.Y = y;
bool finalise = false;
this.SelectionFunction.Initialize(alpha, gradient);
while (finalise == false && iterations < this.MaxIterations)
{
changes = 0;
#region Training
for (int p = 0; p < m; p++)
{
// get new working set selection using heuristic function
Tuple<int, int> newPair = this.SelectionFunction.GetWorkingSet(i, j, gradient, alpha);
// check for valid i, j pairs
if (newPair.Item1 >= 0 && newPair.Item2 >= 0 && newPair.Item1 != newPair.Item2)
{
i = newPair.Item1; j = newPair.Item2;
// compute new gradients
gradient[i] = Bias + (alpha * y * K[i, VectorType.Col]).Sum() - y[i];
if ((y[i] * gradient[i] < -this.Epsilon && alpha[i] < this.C) || (y[i] * gradient[i] > this.Epsilon && alpha[i] > 0))
{
gradient[j] = Bias + (alpha * y * K[j, VectorType.Col]).Sum() - y[j];
// store temp working copies of alpha from both pairs (i, j)
tempAI = alpha[i]; tempAJ = alpha[j];
// update lower and upper bounds of lagrange multipliers
if (y[i] == y[j])
{
// pairs are same class don't apply large margin
lagLow = System.Math.Max(0.0, alpha[j] + alpha[i] - this.C);
lagHigh = System.Math.Min(this.C, alpha[j] + alpha[i]);
}
else
{
// pairs are not same class, apply large margin
lagLow = System.Math.Max(0.0, alpha[j] - alpha[i]);
lagHigh = System.Math.Min(this.C, this.C + alpha[j] - alpha[i]);
}
// if lagrange constraints are not diverse then get new working set
if (lagLow == lagHigh) continue;
// compute cost and if it's greater than 0 skip
// cost should optimise large margin where fit line intercepts <= 0
cost = 2.0 * K[i, j] - K[i, i] - K[j, j];
if (cost >= 0.0) continue;
else
{
// update alpha of (j) w.r.t to the relative cost difference of the i-th and j-th gradient
alpha[j] = alpha[j] - (y[j] * (gradient[i] - gradient[j])) / cost;
// clip alpha with lagrange multipliers
alpha[j] = System.Math.Min(lagHigh, alpha[j]);
alpha[j] = System.Math.Max(lagLow, alpha[j]);
// check alpha tolerance factor
if (System.Math.Abs(alpha[j] - tempAJ) < this.Epsilon)
{
// we're optimising large margins so skip small ones
alpha[j] = tempAJ; continue;
}
// update alpha of i if we have a large margin w.r.t to alpha (j)
alpha[i] = alpha[i] + y[i] * y[j] * (tempAJ - alpha[j]);
// precompute i, j into feasible region for Bias
double yBeta = (alpha[i] - tempAI) * K[i, j] - y[j] * (alpha[j] - tempAJ);
// store temp beta with gradient for i, j pairs
double beta_i = this.Bias - gradient[i] - y[i] * yBeta * K[i, j];
double beta_j = this.Bias - gradient[j] - y[i] * yBeta * K[j, j];
// update new bias with constrained alpha limits (0 < alpha < C)
if (0.0 < alpha[i] && alpha[i] < this.C) this.Bias = beta_i;
else if (0.0 < alpha[j] && alpha[j] < this.C) this.Bias = beta_j;
else this.Bias = (beta_i + beta_j) / 2.0;
changes++;
}
}
}
else if (newPair.Item1 == -1 || newPair.Item2 == -1)
{
// unable to find suitable sub problem (j) to optimise
finalise = true;
break;
}
}
if (changes == 0) iterations++;
else iterations = 0;
#endregion
}
// get only supporting parameters where alpha is positive
// i.e. because 0 < alpha < large margin
int[] fitness = (alpha > 0d).ToArray();
// return initialised model
return new SVMModel()
{
Descriptor = this.Descriptor,
FeatureNormalizer = base.FeatureNormalizer,
FeatureProperties = base.FeatureProperties,
Theta = ((alpha * y) * X).ToVector(),
Alpha = alpha.Slice(fitness),
Bias = this.Bias,
X = X.Slice(fitness, VectorType.Row),
Y = y.Slice(fitness),
KernelFunction = this.KernelFunction
};
}
/// <summary>A Matrix extension method that slices.</summary>
/// <param name="m">Matrix.</param>
/// <param name="indices">The indices.</param>
/// <param name="t">Row or Column sum.</param>
/// <returns>A Matrix.</returns>
public static Matrix Slice(this Matrix m, IEnumerable <int> indices, VectorType t)
{
return(Matrix.Slice(m, indices, t));
}
/// <summary>A Matrix extension method that slices.</summary>
/// <param name="m">Matrix.</param>
/// <param name="indices">The indices.</param>
/// <returns>A Matrix.</returns>
public static Matrix Slice(this Matrix m, IEnumerable <int> indices)
{
return(Matrix.Slice(m, indices));
}
/// <summary>Generates a model.</summary>
/// <param name="generator">Model generator used.</param>
/// <param name="x">The Matrix to process.</param>
/// <param name="y">The Vector to process.</param>
/// <param name="examples">Source data.</param>
/// <param name="trainingPct">The training pct.</param>
/// <param name="total">Number of Examples</param>
/// <returns>The model.</returns>
private static LearningModel GenerateModel(IGenerator generator, Matrix x, Vector y, IEnumerable<object> examples, double trainingPct, int total)
{
var descriptor = generator.Descriptor;
//var total = examples.Count();
var trainingCount = (int)System.Math.Floor(total * trainingPct);
// 100 - trainingPercentage for testing
var testingSlice = GetTestPoints(total - trainingCount, total).ToArray();
// trainingPercentage for training
var trainingSlice = GetTrainingPoints(testingSlice, total).ToArray();
// training
var x_t = x.Slice(trainingSlice);
var y_t = y.Slice(trainingSlice);
// generate model
var model = generator.Generate(x_t, y_t);
model.Descriptor = descriptor;
Score score = new Score();
if (testingSlice.Count() > 0)
{
// testing
object[] test = GetTestExamples(testingSlice, examples);
Vector y_pred = new Vector(test.Length);
Vector y_test = descriptor.ToExamples(test).Item2;
bool isBinary = y_test.IsBinary();
if (isBinary)
y_test = y_test.ToBinary(f => f == 1d, 1.0, 0.0);
for (int j = 0; j < test.Length; j++)
{
// items under test
object o = test[j];
// make prediction
var features = descriptor.Convert(o, false).ToVector();
// --- temp changes ---
double val = model.Predict(features);
var pred = descriptor.Label.Convert(val);
var truth = Ject.Get(o, descriptor.Label.Name);
if (truth.Equals(pred))
y_pred[j] = y_test[j];
else
y_pred[j] = (isBinary ? (y_test[j] >= 1d ? 0d : 1d) : val);
}
// score predictions
score = Score.ScorePredictions(y_pred, y_test);
}
return new LearningModel { Generator = generator, Model = model, Score = score };
}
