// Creates the features from the inputs. Features must be nSamples x nFeatures or nil
func FeaturizeTrainable(t Trainable, inputs common.RowMatrix, featurizedInputs *mat64.Dense) *mat64.Dense {
nSamples, nDim := inputs.Dims()
if featurizedInputs == nil {
nFeatures := t.NumFeatures()
featurizedInputs = mat64.NewDense(nSamples, nFeatures, nil)
}
rowViewer, isRowViewer := inputs.(mat64.RowViewer)
var f func(start, end int)
if isRowViewer {
f = func(start, end int) {
featurizer := t.NewFeaturizer()
for i := start; i < end; i++ {
featurizer.Featurize(rowViewer.RowView(i), featurizedInputs.RowView(i))
}
}
} else {
f = func(start, end int) {
featurizer := t.NewFeaturizer()
input := make([]float64, nDim)
for i := start; i < end; i++ {
inputs.Row(input, i)
featurizer.Featurize(input, featurizedInputs.RowView(i))
}
}
}
common.ParallelFor(nSamples, common.GetGrainSize(nSamples, minGrain, maxGrain), f)
return featurizedInputs
}
// LinearLeastSquares computes the least squares fit for the function
//
// f(x) = ╬њРѓђtermsРѓђ(x) + ╬њРѓЂtermsРѓЂ(x) + ...
//
// to the data (xs[i], ys[i]). It returns the parameters ╬њРѓђ, ╬њРѓЂ, ...
// that minimize the sum of the squares of the residuals of f:
//
// РѕЉ (ys[i] - f(xs[i]))┬▓
//
// If weights is non-nil, it is used to weight these residuals:
//
// РѕЉ weights[i] ├Ќ (ys[i] - f(xs[i]))┬▓
//
// The function f is specified by one Go function for each linear
// term. For efficiency, the Go function is vectorized: it will be
// passed a slice of x values in xs and must fill the slice termOut
// with the value of the term for each value in xs.
func LinearLeastSquares(xs, ys, weights []float64, terms ...func(xs, termOut []float64)) (params []float64) {
// The optimal parameters are found by solving for ╬њ╠ѓ in the
// "normal equations":
//
// (ЮљЌрхђЮљќЮљЌ)╬њ╠ѓ = ЮљЌрхђЮљќЮљ▓
//
// where Юљќ is a diagonal weight matrix (or the identity matrix
// for the unweighted case).
// TODO: Consider using orthogonal decomposition.
if len(xs) != len(ys) {
panic("len(xs) != len(ys)")
}
if weights != nil && len(xs) != len(weights) {
panic("len(xs) != len(weights")
}
// Construct ЮљЌрхђ. This is the more convenient representation
// for efficiently calling the term functions.
xTVals := make([]float64, len(terms)*len(xs))
for i, term := range terms {
term(xs, xTVals[i*len(xs):i*len(xs)+len(xs)])
}
XT := mat64.NewDense(len(terms), len(xs), xTVals)
X := XT.T()
// Construct ЮљЌрхђЮљќ.
var XTW *mat64.Dense
if weights == nil {
// Юљќ is the identity matrix.
XTW = XT
} else {
// Since Юљќ is a diagonal matrix, we do this directly.
XTW = mat64.DenseCopyOf(XT)
WDiag := mat64.NewVector(len(weights), weights)
for row := 0; row < len(terms); row++ {
rowView := XTW.RowView(row)
rowView.MulElemVec(rowView, WDiag)
}
}
// Construct Юљ▓.
y := mat64.NewVector(len(ys), ys)
// Compute ╬њ╠ѓ.
lhs := mat64.NewDense(len(terms), len(terms), nil)
lhs.Mul(XTW, X)
rhs := mat64.NewVector(len(terms), nil)
rhs.MulVec(XTW, y)
BVals := make([]float64, len(terms))
B := mat64.NewVector(len(terms), BVals)
B.SolveVec(lhs, rhs)
return BVals
}
func predictFeaturized(featurizedInput []float64, featureWeights *mat64.Dense, output []float64) {
for i := range output {
output[i] = 0
}
for j, zval := range featurizedInput {
for i, weight := range featureWeights.RowView(j) {
output[i] += weight * zval
}
}
}
// Stochastic gradient descent updates the parameters of theta on a random row selection from a matrix.
// It is faster as it does not compute the cost function over the entire dataset every time.
// It instead calculates the error parameters over only one row of the dataset at a time.
// In return, there is a trade off for accuracy. This is minimised by running multiple SGD processes
// (the number of goroutines spawned is specified by the procs variable) in parallel and taking an average of the result.
func StochasticGradientDescent(x, y, theta *mat64.Dense, alpha float64, epoch, procs int) *mat64.Dense {
m, _ := y.Dims()
resultPipe := make(chan *mat64.Dense)
results := make([]*mat64.Dense, 0)
for p := 0; p < procs; p++ {
go func() {
// Is this just a pointer to theta?
thetaCopy := mat64.DenseCopyOf(theta)
for i := 0; i < epoch; i++ {
for k := 0; k < m; k++ {
datXtemp := x.RowView(k)
datYtemp := y.RowView(k)
datX := mat64.NewDense(1, len(datXtemp), datXtemp)
datY := mat64.NewDense(1, 1, datYtemp)
datXFlat := mat64.DenseCopyOf(datX)
datXFlat.TCopy(datXFlat)
datX.Mul(datX, thetaCopy)
datX.Sub(datX, datY)
datXFlat.Mul(datXFlat, datX)
// Horrible hack to get around the fact there is no elementwise division in mat64
xFlatRow, _ := datXFlat.Dims()
gradient := make([]float64, 0)
for i := 0; i < xFlatRow; i++ {
row := datXFlat.RowView(i)
for i := range row {
divd := row[i] / float64(m) * alpha
gradient = append(gradient, divd)
}
}
grows := len(gradient)
grad := mat64.NewDense(grows, 1, gradient)
thetaCopy.Sub(thetaCopy, grad)
}
}
resultPipe <- thetaCopy
}()
}
for {
select {
case d := <-resultPipe:
results = append(results, d)
if len(results) == procs {
return averageTheta(results)
}
}
}
}
// wrapper for predict, assumes all inputs are correct
func predict(input []float64, features *mat64.Dense, b []float64, featureWeights *mat64.Dense, output []float64) {
for i := range output {
output[i] = 0
}
nFeatures, _ := features.Dims()
_, outputDim := featureWeights.Dims()
sqrt2OverD := math.Sqrt(2.0 / float64(nFeatures))
//for i, feature := range features {
for i := 0; i < nFeatures; i++ {
z := computeZ(input, features.RowView(i), b[i], sqrt2OverD)
for j := 0; j < outputDim; j++ {
output[j] += z * featureWeights.At(i, j)
}
}
}
// UnscaleData is a wrapper for unscaling data in parallel.
// TODO: Make this work better so that if there is an error somewhere data isn't changed
func UnscaleData(scaler Scaler, data *mat64.Dense) error {
m := &sync.Mutex{}
var e ErrorList
f := func(start, end int) {
for r := start; r < end; r++ {
errTmp := scaler.Unscale(data.RowView(r))
if errTmp != nil {
m.Lock()
e = append(e, &SliceError{Header: "scale", Idx: r, Err: errTmp})
m.Unlock()
}
}
}
nSamples, _ := data.Dims()
grain := common.GetGrainSize(nSamples, 1, 500)
common.ParallelFor(nSamples, grain, f)
if len(e) != 0 {
return e
}
return nil
}
func MultiHypothesis(x *mat64.Dense, theta *mat64.Vector) *mat64.Vector {
var res mat64.Dense
res.Mul(theta.T(), x)
return res.RowView(0)
}
