mat: add NonZeroDoer interfaces and implementations

Also clean up some documentation and missing type checks related to
tests for NonZeroDoers.

mat/triangular.go

@@ -14,9 +14,14 @@ import (
 
 var (
 	triDense *TriDense
-	_        Matrix        = triDense
-	_        Triangular    = triDense
-	_        RawTriangular = triDense
+	_        Matrix            = triDense
+	_        Triangular        = triDense
+	_        RawTriangular     = triDense
+	_        MutableTriangular = triDense
+
+	_ NonZeroDoer    = triDense
+	_ RowNonZeroDoer = triDense
+	_ ColNonZeroDoer = triDense
 )
 
 const badTriCap = "mat: bad capacity for TriDense"
@@ -28,6 +33,7 @@ type TriDense struct {
 	cap int
 }
 
+// Triangular represents a triangular matrix. Triangular matrices are always square.
 type Triangular interface {
 	Matrix
 	// Triangular returns the number of rows/columns in the matrix and its
@@ -39,10 +45,17 @@ type Triangular interface {
 	TTri() Triangular
 }
 
+// A RawTriangular can return a view of itself as a BLAS Triangular matrix.
 type RawTriangular interface {
 	RawTriangular() blas64.Triangular
 }
 
+// A MutableTriangular can set elements of a triangular matrix.
+type MutableTriangular interface {
+	Triangular
+	SetTri(i, j int, v float64)
+}
+
 var (
 	_ Matrix           = TransposeTri{}
 	_ Triangular       = TransposeTri{}
@@ -455,3 +468,73 @@ func copySymIntoTriangle(t *TriDense, s Symmetric) {
 		}
 	}
 }
+
+// DoNonZero calls the function fn for each of the non-zero elements of t. The function fn
+// takes a row/column index and the element value of t at (i, j).
+func (t *TriDense) DoNonZero(fn func(i, j int, v float64)) {
+	if t.isUpper() {
+		for i := 0; i < t.mat.N; i++ {
+			for j := i; j < t.mat.N; j++ {
+				v := t.at(i, j)
+				if v != 0 {
+					fn(i, j, v)
+				}
+			}
+		}
+		return
+	}
+	for i := 0; i < t.mat.N; i++ {
+		for j := 0; j <= i; j++ {
+			v := t.at(i, j)
+			if v != 0 {
+				fn(i, j, v)
+			}
+		}
+	}
+}
+
+// DoRowNonZero calls the function fn for each of the non-zero elements of row i of t. The function fn
+// takes a row/column index and the element value of t at (i, j).
+func (t *TriDense) DoRowNonZero(i int, fn func(i, j int, v float64)) {
+	if i < 0 || t.mat.N <= i {
+		panic(ErrRowAccess)
+	}
+	if t.isUpper() {
+		for j := i; j < t.mat.N; j++ {
+			v := t.at(i, j)
+			if v != 0 {
+				fn(i, j, v)
+			}
+		}
+		return
+	}
+	for j := 0; j <= i; j++ {
+		v := t.at(i, j)
+		if v != 0 {
+			fn(i, j, v)
+		}
+	}
+}
+
+// DoColNonZero calls the function fn for each of the non-zero elements of column j of t. The function fn
+// takes a row/column index and the element value of t at (i, j).
+func (t *TriDense) DoColNonZero(j int, fn func(i, j int, v float64)) {
+	if j < 0 || t.mat.N <= j {
+		panic(ErrColAccess)
+	}
+	if t.isUpper() {
+		for i := 0; i <= j; i++ {
+			v := t.at(i, j)
+			if v != 0 {
+				fn(i, j, v)
+			}
+		}
+		return
+	}
+	for i := j; i < t.mat.N; i++ {
+		v := t.at(i, j)
+		if v != 0 {
+			fn(i, j, v)
+		}
+	}
+}