fix(linalg): refuse non-finite input in dense Cholesky, Eigen and rank-one updates

Assisted-by: GLM 5.3 Flash

linalg/decomp3_test.go

@@ -6,9 +6,11 @@ package linalg
 import (
 	"math"
 	"math/cmplx"
+	"strings"
+	"testing"
+
 	"sourcedock.dev/petrbalvin/tensor/internal/base"
 	"sourcedock.dev/petrbalvin/tensor/internal/core"
-	"testing"
 )
 
 func mustComplexes(t *testing.T, vals []complex128, shape ...int) *core.Array {
@@ -291,3 +293,20 @@ func subComplex(a, b []complex128) []complex128 {
 	}
 	return out
 }
+
+// TestEigenComplexRefusesNonFinite pins that a poisoned matrix never
+// reads as Hermitian: the mirror comparison cannot see a NaN
+// difference, so the entry is refused outright, the way the sparse
+// sibling's Hermitian check refuses it.
+func TestEigenComplexRefusesNonFinite(t *testing.T) {
+	cv := []complex128{complex(math.NaN(), 0), 0, 0, 1}
+	a := mustComplexes(t, cv, 2, 2)
+	if _, _, err := EigenComplex(a); err == nil || !strings.Contains(err.Error(), "not finite") {
+		t.Fatalf("EigenComplex(NaN): %v", err)
+	}
+	cv2 := []complex128{complex(0, math.Inf(1)), 0, 0, 1}
+	b := mustComplexes(t, cv2, 2, 2)
+	if _, _, err := EigenComplex(b); err == nil || !strings.Contains(err.Error(), "not finite") {
+		t.Fatalf("EigenComplex(Inf): %v", err)
+	}
+}