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Estate-wide consolidation pass. golangci-lint v2 default set enables NO formatter, so gofmt drift accumulated silently across the estate -- 8 repos were carrying it, this one included. Same hole that let two files rot in dma-cli until they were found by hand (dma-cli#12). Mechanical and deterministic: `gofmt -w`, nothing hand-edited. Verified before commit -- gofmt -l now reports 0, go build and go vet both pass. Clears this repo to adopt the canonical .golangci.yml (infra ci-templates/golangci.yml, infra#309 pattern) in a later wave.
109 lines
2.7 KiB
Go
109 lines
2.7 KiB
Go
package eval
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import "math"
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// VaRBreachRate computes the parametric 99% VaR breach rate and Kupiec POF p-value.
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//
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// VaR_99_t = predVol[t] × z99 (z99 = 2.326 for 99% normal VaR)
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// breach_t = actualVol[t] > VaR_99_t (strict inequality)
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// breachRate = fraction of breaches over all steps
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// kupiecP = Kupiec POF p-value: P(chi²(1) > LR) where LR is the likelihood ratio
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//
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// testing H0: true breach probability = 1%. High p = well-calibrated.
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//
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// Returns (0, 1) for empty or mismatched input.
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func VaRBreachRate(predVol, actualVol []float64, z99 float64) (breachRate, kupiecP float64) {
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n := len(predVol)
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if n == 0 || n != len(actualVol) {
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return 0, 1
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}
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var n1 int
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for i := 0; i < n; i++ {
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if actualVol[i] > predVol[i]*z99 {
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n1++
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}
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}
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breachRate = float64(n1) / float64(n)
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kupiecP = kupiecPOF(n, n1, 0.01)
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return
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}
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// kupiecPOF returns the Kupiec Proportion-of-Failures p-value.
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// H0: true breach probability = p0 (e.g. 0.01 for 99% VaR).
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// Returns 1.0 for edge cases (n=0, p_hat=p0).
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func kupiecPOF(n, n1 int, p0 float64) float64 {
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if n == 0 {
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return 1.0
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}
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n0 := n - n1
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phat := float64(n1) / float64(n)
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var lr float64
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switch n1 {
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case 0:
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// 0 × ln(0/p0) = 0 by convention; only the n0 term contributes
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lr = 2 * float64(n0) * math.Log((1-phat)/(1-p0))
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case n:
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// n0 term vanishes
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lr = 2 * float64(n1) * math.Log(phat/p0)
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default:
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lr = 2 * (float64(n1)*math.Log(phat/p0) + float64(n0)*math.Log((1-phat)/(1-p0)))
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}
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if lr <= 0 {
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return 1.0
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}
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// P(chi²(1) > LR) = erfc(sqrt(LR/2)) [chi²(1) = Z², Z~N(0,1)]
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return math.Erfc(math.Sqrt(lr / 2))
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}
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// LinearProbePredict fits ridge regression on (trainEmb, trainY) and returns
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// predictions for testEmb. Complements LinearProbeTrainTest when the caller
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// needs the raw predictions (e.g. to compute VaR breach rate).
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// Returns nil when trainEmb is empty.
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func LinearProbePredict(trainEmb [][]float64, trainY []float64,
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testEmb [][]float64, lambda float64) []float64 {
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n := len(trainEmb)
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if n == 0 || len(testEmb) == 0 {
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return nil
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}
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d := len(trainEmb[0])
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p := d + 1
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A := make([][]float64, n)
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for i, e := range trainEmb {
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row := make([]float64, p)
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copy(row, e)
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row[d] = 1.0
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A[i] = row
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}
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AtA := make([][]float64, p)
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for i := range AtA {
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AtA[i] = make([]float64, p)
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}
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Aty := make([]float64, p)
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for i := 0; i < n; i++ {
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for j := 0; j < p; j++ {
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Aty[j] += A[i][j] * trainY[i]
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for k := 0; k < p; k++ {
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AtA[j][k] += A[i][j] * A[i][k]
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}
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}
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}
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for j := 0; j < p; j++ {
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AtA[j][j] += lambda
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}
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w := solveCholesky(AtA, Aty)
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preds := make([]float64, len(testEmb))
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for i, e := range testEmb {
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row := make([]float64, p)
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copy(row, e)
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row[d] = 1.0
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preds[i] = dot(row, w)
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}
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return preds
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}
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