// Calculates the variance-covariance matrix of the regression coefficients
// defined as sigma*(XtX)-1
// Using QR decomposition: X = QR
// ((QR)tQR)-1 ---> (RtQtQR)-1 ---> (RtR)-1 ---> R-1Rt-1 --> sigma*R-1Rt-1
//
func (o *OLS) VarianceCovarianceMatrix() *mat64.Dense {
x := mat64.DenseCopyOf(o.x.data)
_, p := x.Dims()
// it's easier to do things with X = QR
qrFactor := mat64.QR(x)
R := qrFactor.R()
Rt := R.T()
RtInv, err := mat64.Inverse(Rt)
if err != nil {
panic("Rt is not invertible")
}
Rinverse, err := mat64.Inverse(R)
if err != nil {
panic("R matrix is not invertible")
}
varCov := mat64.NewDense(p, p, nil)
varCov.Mul(Rinverse, RtInv)
// multiple each element by the mse
mse := o.MeanSquaredError()
mulEach := func(r, c int, v float64) float64 { return v * mse }
varCov.Apply(mulEach, varCov)
return varCov
}
func (lr *LinearRegression) Fit(inst *base.Instances) error {
if inst.Rows < inst.GetAttributeCount() {
return NotEnoughDataError
}
// Split into two matrices, observed results (dependent variable y)
// and the explanatory variables (X) - see http://en.wikipedia.org/wiki/Linear_regression
observed := mat64.NewDense(inst.Rows, 1, nil)
explVariables := mat64.NewDense(inst.Rows, inst.GetAttributeCount(), nil)
for i := 0; i < inst.Rows; i++ {
observed.Set(i, 0, inst.Get(i, inst.ClassIndex)) // Set observed data
for j := 0; j < inst.GetAttributeCount(); j++ {
if j == 0 {
// Set intercepts to 1.0
// Could / should be done better: http://www.theanalysisfactor.com/interpret-the-intercept/
explVariables.Set(i, 0, 1.0)
} else {
explVariables.Set(i, j, inst.Get(i, j-1))
}
}
}
n := inst.GetAttributeCount()
qr := mat64.QR(explVariables)
q := qr.Q()
reg := qr.R()
var transposed, qty mat64.Dense
transposed.TCopy(q)
qty.Mul(&transposed, observed)
regressionCoefficients := make([]float64, n)
for i := n - 1; i >= 0; i-- {
regressionCoefficients[i] = qty.At(i, 0)
for j := i + 1; j < n; j++ {
regressionCoefficients[i] -= regressionCoefficients[j] * reg.At(i, j)
}
regressionCoefficients[i] /= reg.At(i, i)
}
lr.disturbance = regressionCoefficients[0]
lr.regressionCoefficients = regressionCoefficients[1:]
lr.fitted = true
return nil
}
func (o *OLS) Train(yvector []float64) error {
// sanity check
if len(yvector) != o.n {
return DimensionError
}
copy(o.response, yvector)
y := mat64.NewDense(len(yvector), 1, yvector)
o.x.PushCol(rep(1.0, o.x.rows))
x := o.x.data
// it's easier to do things with X = QR
qrFactor := mat64.QR(mat64.DenseCopyOf(x))
Q := qrFactor.Q()
betas := qrFactor.Solve(mat64.DenseCopyOf(y))
o.betas = betas.Col(nil, 0)
if len(o.betas) != o.p {
log.Printf("Unexpected dimension error. Betas: %v", o.betas)
}
// calculate residuals and fitted vals
/*
fitted := &mat64.Dense{}
fitted.Mul(x, betas)
o.fitted = fitted.Col(nil, 0)
y.Sub(y, fitted)
o.residuals = y.Col(nil, 0)
*/
// y_hat = Q Qt y
// e = y - y_hat
qqt := &mat64.Dense{}
qqt.Mul(Q, Q.T())
yhat := &mat64.Dense{}
yhat.Mul(qqt, y)
o.fitted = yhat.Col(nil, 0)
y.Sub(y, yhat)
o.residuals = y.Col(nil, 0)
return nil
}
// Leverage Points, the diagonal of the hat matrix
// H = X(X'X)^-1X' , X = QR, X' = R'Q'
// = QR(R'Q'QR)-1 R'Q'
// = QR(R'R)-1 R'Q'
// = QRR'-1 R-1 R'Q'
// = QQ' (the first p cols of Q, where X = n x p)
//
// Leverage points are considered large if they exceed 2p/ n
func (o *OLS) LeveragePoints() []float64 {
x := mat64.DenseCopyOf(o.x.data)
qrf := mat64.QR(x)
q := qrf.Q()
H := &mat64.Dense{}
H.Mul(q, q.T())
o.hat = H
// get diagonal elements
n, _ := q.Dims()
diag := make([]float64, n)
for i := 0; i < n; i++ {
for j := 0; j < n; j++ {
if j == i {
diag[i] = H.At(i, j)
}
}
}
return diag
}
func main() {
x, y := givens()
fmt.Printf("%.4f\n", mat64.Formatted(mat64.QR(x).Solve(y)))
}
func (lr *LinearRegression) Fit(inst base.FixedDataGrid) error {
// Retrieve row size
_, rows := inst.Size()
// Validate class Attribute count
classAttrs := inst.AllClassAttributes()
if len(classAttrs) != 1 {
return fmt.Errorf("Only 1 class variable is permitted")
}
classAttrSpecs := base.ResolveAttributes(inst, classAttrs)
// Retrieve relevant Attributes
allAttrs := base.NonClassAttributes(inst)
attrs := make([]base.Attribute, 0)
for _, a := range allAttrs {
if _, ok := a.(*base.FloatAttribute); ok {
attrs = append(attrs, a)
}
}
cols := len(attrs) + 1
if rows < cols {
return NotEnoughDataError
}
// Retrieve relevant Attribute specifications
attrSpecs := base.ResolveAttributes(inst, attrs)
// Split into two matrices, observed results (dependent variable y)
// and the explanatory variables (X) - see http://en.wikipedia.org/wiki/Linear_regression
observed := mat64.NewDense(rows, 1, nil)
explVariables := mat64.NewDense(rows, cols, nil)
// Build the observed matrix
inst.MapOverRows(classAttrSpecs, func(row [][]byte, i int) (bool, error) {
val := base.UnpackBytesToFloat(row[0])
observed.Set(i, 0, val)
return true, nil
})
// Build the explainatory variables
inst.MapOverRows(attrSpecs, func(row [][]byte, i int) (bool, error) {
// Set intercepts to 1.0
explVariables.Set(i, 0, 1.0)
for j, r := range row {
explVariables.Set(i, j+1, base.UnpackBytesToFloat(r))
}
return true, nil
})
n := cols
qr := mat64.QR(explVariables)
q := qr.Q()
reg := qr.R()
var transposed, qty mat64.Dense
transposed.TCopy(q)
qty.Mul(&transposed, observed)
regressionCoefficients := make([]float64, n)
for i := n - 1; i >= 0; i-- {
regressionCoefficients[i] = qty.At(i, 0)
for j := i + 1; j < n; j++ {
regressionCoefficients[i] -= regressionCoefficients[j] * reg.At(i, j)
}
regressionCoefficients[i] /= reg.At(i, i)
}
lr.disturbance = regressionCoefficients[0]
lr.regressionCoefficients = regressionCoefficients[1:]
lr.fitted = true
lr.attrs = attrs
lr.cls = classAttrs[0]
return nil
}
