p3: add lrls/helper.go

p3/go.mod

@@ -4,4 +4,4 @@ go 1.19
 
 require git.dotya.ml/wanderer/ak9im/p2 v0.0.0-20230227032746-9910d7702660
 
-require gonum.org/v1/gonum v0.12.0 // indirect
+require gonum.org/v1/gonum v0.12.0

p3/lrls/helper.go

@@ -0,0 +1,58 @@
+package lrls
+
+import (
+	"errors"
+	"log"
+
+	"gonum.org/v1/gonum/mat"
+)
+
+// diagMat returns a Diagonal Matrix initialised with *data* across the main
+// diagonal.
+// nolint: unused
+func diagMat(data []float64) *mat.DiagDense {
+	n := len(data)
+
+	dm := mat.NewDiagDense(n, data)
+
+	return dm
+}
+
+// nolint: unused
+func diagVals(n int) []float64 {
+	d := make([]float64, n)
+
+	for i := 0; i < n; i++ {
+		d[i] = 1000000
+	}
+
+	return d
+}
+
+// nolint: unused
+func covMatrices(size, params int) ([]*mat.Dense, error) {
+	switch {
+	case size < 1:
+		return nil, errors.New("ErrCovMatricesSize")
+
+	case params < 4 || params > 5:
+		log.Printf("error: params needs to be from the set {4 ,5}, got: %d", params)
+		return nil, errors.New("ErrBadParams")
+	}
+
+	// slice of covariance matrices.
+	cms := make([]*mat.Dense, 0, size)
+
+	for i := range cms {
+		cms[i] = mat.NewDense(params, params, nil)
+	}
+
+	// create a matrix of the same shape as the cov matrix, with *diagVals*
+	// along the main diagonal.
+	dm := diagMat(diagVals(params))
+
+	// replace the second covariance matrix with the diagonal matrix.
+	cms[1].CloneFrom(dm)
+
+	return cms, nil
+}