optimize: remove lint found by megacheck

optimize/convex/lp/simplex.go

@@ -537,7 +537,7 @@ func findInitialBasic(A mat64.Matrix, b []float64) ([]int, *mat64.Dense, []float
 	// Solve the Phase I linear program.
 	_, xOpt, newBasic, err := simplex(basicIdxs, c, aNew, b, 1e-10)
 	if err != nil {
-		return nil, nil, nil, errors.New(fmt.Sprintf("lp: error finding feasible basis: %s", err))
+		return nil, nil, nil, fmt.Errorf("lp: error finding feasible basis: %s", err)
 	}
 
 	// The original LP is infeasible if the added variable has non-zero value

optimize/global.go

@@ -156,7 +156,6 @@ type globalStatus struct {
 	startTime time.Time
 	optLoc    *Location
 	settings  *Settings
-	method    GlobalMethod
 	statuser  Statuser
 	err       error
 }

optimize/minimize.go

@@ -50,7 +50,7 @@ func copyLocation(dst, src *Location) {
 
 func checkOptimization(p Problem, dim int, method Needser, recorder Recorder) error {
 	if p.Func == nil {
-		panic("optimize: objective function is undefined")
+		panic(badProblem)
 	}
 	if dim <= 0 {
 		panic("optimize: impossible problem dimension")

optimize/unconstrained_test.go

@@ -998,7 +998,7 @@ func TestLocal(t *testing.T) {
 	// Mix of functions with and without Grad method.
 	tests = append(tests, gradFreeTests...)
 	tests = append(tests, gradientDescentTests...)
-	testLocal(t, gradientDescentTests, nil)
+	testLocal(t, tests, nil)
 }
 
 func TestNelderMead(t *testing.T) {