mathtools/cmd/divisors.go

/*
Copyright © 2025 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 (
	"fmt"

	"github.com/spf13/cobra"
	"scm.dairydemon.net/filifa/mathtools/internal/lib"
)

var divisorsN uint
var divisorsE uint

func divisors(cmd *cobra.Command, args []string) {
	ch := lib.DivisorsSieve(divisorsN, divisorsE)
	for i := 0; ; i++ {
		v, ok := <-ch
		if !ok {
			break
		}

		if i == 0 {
			continue
		}

		fmt.Println(v)
	}
}

// divisorsCmd represents the divisors command
var divisorsCmd = &cobra.Command{
	Use:   "divisors -n N",
	Short: "Compute the divisor function for all numbers less than n",
	Long: `Compute the divisor function for all numbers less than n.

sigma_x(n) computes the sum of the xth powers of the divisors of n.
For example, the divisors of 12 are 1, 2, 3, 4, 6, and 12.
sigma_0(12) = 6
sigma_1(12) = 1 + 2 + 3 + 4 + 6 + 12 = 28
sigma_2(12) = 1^2 + 2^2 + 3^2 + 4^2 + 6^2 + 12^2 = 210

This program computes sigma for all values less than the input n.
Provide the --exponent flag to set the desired exponent for each sum.`,
	Run: divisors,
}

func init() {
	sieveCmd.AddCommand(divisorsCmd)

	// Here you will define your flags and configuration settings.

	// Cobra supports Persistent Flags which will work for this command
	// and all subcommands, e.g.:
	// divisorsCmd.PersistentFlags().String("foo", "", "A help for foo")

	// Cobra supports local flags which will only run when this command
	// is called directly, e.g.:
	// divisorsCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")

	divisorsCmd.Flags().UintVarP(&divisorsN, "limit", "n", 0, "upper limit")
	divisorsCmd.MarkFlagRequired("limit")

	divisorsCmd.Flags().UintVarP(&divisorsE, "exponent", "e", 0, "exponent")
}