Changed add method to have the first element be a slice

examples_test.go

@@ -6,13 +6,78 @@ import (
 
 // Set of examples for all the functions
 
-func ExampleAdd() {
+func ExampleAdd_Simple() {
+	// Adding three slices together. Note that
+	// the result is stored in the first slice
 	s1 := []float64{1, 2, 3, 4}
 	s2 := []float64{5, 6, 7, 8}
-	Add(s1, s2)
+	s3 := []float64{1, 1, 1, 1}
+
+	Add(s1, s2, s3)
+
 	fmt.Println("s1 = ", s1)
 	fmt.Println("s2 = ", s2)
+	fmt.Println("s3 = ", s3)
 	// Output:
-	// s1 =  [6 8 10 12]
+	// s1 =  [7 9 11 13]
 	// s2 =  [5 6 7 8]
+	// s3 =  [1 1 1 1]
+}
+
+func ExampleAdd_NewSlice() {
+	// If one wants to store the result in a
+	// new container, just make a new slice
+	s1 := []float64{1, 2, 3, 4}
+	s2 := []float64{5, 6, 7, 8}
+	s3 := []float64{1, 1, 1, 1}
+	dst := make([]float64, len(s1))
+
+	Add(dst, s1, s2, s3)
+
+	fmt.Println("dst = ", dst)
+	fmt.Println("s1 = ", s1)
+	fmt.Println("s2 = ", s2)
+	fmt.Println("s3 = ", s3)
+	// Output:
+	// dst =  [7 9 11 13]
+	// s1 =  [1 2 3 4]
+	// s2 =  [5 6 7 8]
+	// s3 =  [1 1 1 1]
+}
+
+func ExampleAdd_UnequalLengths() {
+	// If the lengths of the slices are unknown,
+	// use Eqlen to check
+	s1 := []float64{1, 2, 3}
+	s2 := []float64{5, 6, 7, 8}
+
+	eq := Eqlen(s1, s2)
+	if eq {
+		Add(s1, s2)
+	} else {
+		fmt.Println("Unequal lengths")
+	}
+	// Output:
+	// Unequal lengths
+}
+
+func ExampleAdd_SliceOfSliceSum() {
+	// Add can also be used to take a columnwise sum
+	// of a slice of slices
+
+	// First, initialize a slice of slices
+	s := make([][]float64, 5)
+	for i := range s {
+		s[i] = make([]float64, 3)
+		for j := range s[i] {
+			s[i][j] = float64(j)
+		}
+	}
+	// Remember that the first entry is the destination
+	result := make([]float64, len(s[0]))
+	Add(result, s...)
+
+	fmt.Println("result = ", result)
+	// Output:
+	// result =  [0 5 10]
 }

sliceops.go

@@ -16,13 +16,13 @@ func (i InsufficientElements) Error() string {
 // For computational efficiency, it is assumed that all of
 // the variadic arguments have the same length. If this is
 // in doubt, EqLengths can be called.
-func Add(slices ...[]float64) {
+func Add(dst []float64, slices ...[]float64) {
 	if len(slices) == 0 {
 		return
 	}
-	for i := 1; i < len(slices); i++ {
+	for i := 0; i < len(slices); i++ {
 		for j, val := range slices[i] {
-			slices[0][j] += val
+			dst[j] += val
 		}
 	}
 }

sliceops_test.go

@@ -17,7 +17,7 @@ const (
 
 func AreSlicesEqual(t *testing.T, truth, comp []float64, str string) {
 	if !Eq(comp, truth, EQTOLERANCE) {
-		t.Errorf(str+"Expected %v, returned %v", truth, comp)
+		t.Errorf(str+". Expected %v, returned %v", truth, comp)
 	}
 }
 
@@ -367,7 +367,7 @@ func BenchmarkMinHuge(b *testing.B) {
 func benchmarkAdd(b *testing.B, s ...[]float64) {
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
-		Add(s...)
+		Add(s[0], s[1:]...)
 	}
 }