Add dgetrf and tests

removed unnecessary requirement

Implement Dlaswp in both directions

Responded to PR comments

testlapack/dgetrf.go

@@ -0,0 +1,60 @@
+package testlapack
+
+import (
+	"math/rand"
+	"testing"
+)
+
+type Dgetrfer interface {
+	Dgetrf(m, n int, a []float64, lda int, ipiv []int) bool
+}
+
+func DgetrfTest(t *testing.T, impl Dgetrfer) {
+	for _, test := range []struct {
+		m, n, lda int
+	}{
+		{10, 5, 0},
+		{5, 10, 0},
+		{10, 10, 0},
+		{300, 5, 0},
+		{3, 500, 0},
+		{4, 5, 0},
+		{300, 200, 0},
+		{204, 300, 0},
+		{1, 3000, 0},
+		{3000, 1, 0},
+		{10, 5, 20},
+		{5, 10, 20},
+		{10, 10, 20},
+		{300, 5, 400},
+		{3, 500, 600},
+		{200, 200, 300},
+		{300, 200, 300},
+		{204, 300, 400},
+		{1, 3000, 4000},
+		{3000, 1, 4000},
+	} {
+		m := test.m
+		n := test.n
+		lda := test.lda
+		if lda == 0 {
+			lda = n
+		}
+		a := make([]float64, m*lda)
+		for i := range a {
+			a[i] = rand.Float64()
+		}
+		mn := min(m, n)
+		ipiv := make([]int, mn)
+		for i := range ipiv {
+			ipiv[i] = rand.Int()
+		}
+
+		// Cannot compare the outputs of Dgetrf and Dgetf2 because the pivoting may
+		// happen differently. Instead check that the LPQ factorization is correct.
+		aCopy := make([]float64, len(a))
+		copy(aCopy, a)
+		ok := impl.Dgetrf(m, n, a, lda, ipiv)
+		checkPLU(t, ok, m, n, lda, ipiv, a, aCopy, 1e-10, false)
+	}
+}