Update NewtonKrylov.Solve signature (#20)

This commit updates the NewtonKrylov.Solve method to propagate
error when max iterations are reached and there is no convergence.

resolves #19

examples/burger/main.go

@@ -6,6 +6,7 @@ import (
 	"encoding/csv"
 	"flag"
 	"fmt"
+	"log"
 	"math"
 	"os"
 
@@ -51,10 +52,15 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	defer csvfile.Close()
+
 	csvwriter := csv.NewWriter(csvfile)
 	for i := 0; i < *steps; i++ {
 		copy(uCpy, u)
-		res := solver.Solve(problem, u)
+		res, err := solver.Solve(problem, u)
+		if err != nil {
+			log.Fatal(err)
+		}
 		copy(u, res.X)
 
 		row := make([]string, len(u))
@@ -64,5 +70,5 @@ func main() {
 		csvwriter.Write(row)
 	}
 	csvwriter.Flush()
-	csvfile.Close()
+
 }

nonlin/newtonKrylov.go

@@ -49,7 +49,7 @@ type NewtonKrylov struct {
 // Solve solves the non-linear system of equations. The method terminates when
 // the inifinity norm of F + the inifinity norm of dx is less than the tolerance.
 // dx is the change in x between two sucessive iterations.
-func (nk *NewtonKrylov) Solve(p Problem, x []float64) Result {
+func (nk *NewtonKrylov) Solve(p Problem, x []float64) (Result, error) {
 	var deriv DerivativeApprox
 	switch nk.Stencil {
 	case 0, 4:
@@ -85,7 +85,8 @@ func (nk *NewtonKrylov) Solve(p Problem, x []float64) Result {
 		}
 		res, err := linsolve.Iterative(&deriv, b, nk.InnerMethod, nk.InnerSettings)
 		if err != nil {
-			log.Fatalf("NewtonKrylov: %s\n", err)
+			log.Printf("[ERROR] NewtonKrylov: %s\n", err)
+			return Result{}, err
 		}
 
 		if InfNorm(f0)+mat.Norm(res.X, math.Inf(1)) < nk.Tol {
@@ -94,7 +95,7 @@ func (nk *NewtonKrylov) Solve(p Problem, x []float64) Result {
 				Converged: true,
 				MaxF:      InfNorm(f0),
 				F:         f0,
-			}
+			}, nil
 		}
 
 		// Update x
@@ -123,5 +124,5 @@ func (nk *NewtonKrylov) Solve(p Problem, x []float64) Result {
 		Converged: false,
 		MaxF:      InfNorm(f0),
 		F:         f0,
-	}
+	}, nil
 }

nonlin/newtonKrylov_test.go

@@ -70,7 +70,10 @@ func TestBicStab(t *testing.T) {
 		p := Problem{
 			F: test.F,
 		}
-		res := solver.Solve(p, test.Init)
+		res, err := solver.Solve(p, test.Init)
+		if err != nil {
+			t.Error(err)
+		}
 
 		if !res.Converged {
 			t.Errorf("Test #%d did not converged", i)

nonlin/nonlin_example_test.go

@@ -3,11 +3,12 @@ package nonlin_test
 import (
 	"fmt"
 	"math"
+	"testing"
 
 	"github.com/davidkleiven/gononlin/nonlin"
 )
 
-func ExampleNewtonKrylov() {
+func ExampleNewtonKrylov(t *testing.T) {
 	// This example shows how one can use NewtonKrylov to solve the
 	// system of equations
 	// (x-1)^2*(x - y) = 0
@@ -32,7 +33,10 @@ func ExampleNewtonKrylov() {
 	}
 
 	x0 := []float64{0.0, 3.0}
-	res := solver.Solve(problem, x0)
+	res, err := solver.Solve(problem, x0)
+	if err != nil {
+		t.Error(err)
+	}
 	fmt.Printf("Root: (x, y) = (%.2f, %.2f)\n", res.X[0], res.X[1])
 	fmt.Printf("Function value: (%.2f, %.2f)\n", res.F[0], res.F[1])