add convolve command

cmd/common.go

@@ -0,0 +1,32 @@
+/*
+Copyright © 2026 filifa
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+package cmd
+
+import (
+	"bufio"
+	"os"
+)
+
+func splitLines(file *os.File) []string {
+	slice := make([]string, 0)
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		slice = append(slice, scanner.Text())
+	}
+
+	return slice
+}

cmd/convolve.go

@@ -0,0 +1,110 @@
+/*
+Copyright © 2026 filifa
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+package cmd
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+
+	"github.com/spf13/cobra"
+	"scm.dairydemon.net/filifa/mathtools/internal/lib"
+)
+
+var convolveA string
+var convolveB string
+
+func readSequenceFromFile(filepath string) ([]complex128, error) {
+	// initial length 1 so index math works
+	seq := make([]complex128, 1)
+	file, err := os.Open(filepath)
+	if err != nil {
+		return seq, err
+	}
+	defer file.Close()
+
+	lines := splitLines(file)
+	for _, line := range lines {
+		x, err := strconv.ParseComplex(line, 128)
+		if err != nil {
+			return seq, err
+		}
+
+		seq = append(seq, x)
+	}
+
+	return seq, nil
+}
+
+func convolve(cmd *cobra.Command, args []string) {
+	a, err := readSequenceFromFile(convolveA)
+	if err != nil {
+		cobra.CheckErr(err)
+	}
+
+	b, err := readSequenceFromFile(convolveB)
+	if err != nil {
+		cobra.CheckErr(err)
+	}
+
+	bufStdout := bufio.NewWriter(os.Stdout)
+	defer bufStdout.Flush()
+
+	for i, n := range lib.DirichletConvolve(a, b) {
+		if i == 0 {
+			continue
+		}
+
+		if imag(n) == 0 {
+			fmt.Fprintln(bufStdout, real(n))
+		} else {
+			fmt.Fprintln(bufStdout, n)
+		}
+	}
+}
+
+// convolveCmd represents the convolve command
+var convolveCmd = &cobra.Command{
+	Use:   "convolve",
+	Short: "Compute the Dirichlet convolution of two sequences",
+	Long: `Compute the Dirichlet convolution of two sequences.
+
+Each sequence is provided as a file, where line k of the file gives the kth term of the sequence.
+`,
+	Run: convolve,
+}
+
+func init() {
+	rootCmd.AddCommand(convolveCmd)
+
+	// Here you will define your flags and configuration settings.
+
+	// Cobra supports Persistent Flags which will work for this command
+	// and all subcommands, e.g.:
+	// convolveCmd.PersistentFlags().String("foo", "", "A help for foo")
+
+	// Cobra supports local flags which will only run when this command
+	// is called directly, e.g.:
+	// convolveCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+
+	convolveCmd.Flags().StringVarP(&convolveA, "first", "a", "", "first sequence")
+	convolveCmd.MarkFlagRequired("first")
+
+	convolveCmd.Flags().StringVarP(&convolveB, "second", "b", "", "second sequence")
+	convolveCmd.MarkFlagRequired("second")
+}

cmd/shoelace.go

@@ -17,7 +17,6 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
-	"bufio"
 	"fmt"
 	"os"
 	"strconv"
@@ -29,16 +28,6 @@ import (
 
 var shoelaceFile string
 
-func splitLines(file *os.File) []string {
-	slice := make([]string, 0)
-	scanner := bufio.NewScanner(file)
-	for scanner.Scan() {
-		slice = append(slice, scanner.Text())
-	}
-
-	return slice
-}
-
 func readFromFile(filepath string) ([]lib.Point, error) {
 	points := make([]lib.Point, 0)
 	file, err := os.Open(filepath)

internal/lib/convolve.go

@@ -0,0 +1,32 @@
+/*
+Copyright © 2026 filifa
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+package lib
+
+func DirichletConvolve(a, b []complex128) []complex128 {
+	c := make([]complex128, min(len(a), len(b)))
+	for i, x := range a {
+		for j, y := range b {
+			if i*j >= len(c) {
+				break
+			}
+
+			c[i*j] += x * y
+		}
+	}
+
+	return c
+}