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

Assisted-by: GLM 5.3 Flash

linalg/decomp3.go

@@ -55,6 +55,18 @@ func EigenComplex(a *core.Array) (values, vectors *core.Array, err error) {
 	if !hermitianOK(h, n) {
 		return nil, nil, base.Errf("EigenComplex: matrix is not Hermitian within 1e-12 tolerance")
 	}
+	// A non-finite entry slips through the Hermitian test above: the
+	// difference of a NaN and its conjugate never exceeds the tolerance.
+	// The sparse twin refuses it in its own guard, and so does this one,
+	// before the Jacobi sweep burns its passes on a poisoned matrix.
+	for i := range n {
+		for j := range n {
+			z := h[i*n+j]
+			if math.IsNaN(real(z)) || math.IsNaN(imag(z)) || math.IsInf(real(z), 0) || math.IsInf(imag(z), 0) {
+				return nil, nil, base.Errf("EigenComplex: entry [%d,%d] is not finite", i, j)
+			}
+		}
+	}
 	// The Jacobi sweep's convergence test is a sum of squared
 	// magnitudes: outside the safe window it overflows to +Inf, which
 	// makes every sweep look already converged, or underflows to 0,