mathtools/cmd/convergents.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"
	"math/big"

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

func convergents(cmd *cobra.Command, args []string) {
	a0, ok := new(big.Int).SetString(args[0], 10)
	if !ok {
		cobra.CheckErr("invalid input " + args[0])
	}

	denoms := make([]*big.Int, len(args[1:]))
	for i, d := range args[1:] {
		denoms[i] = new(big.Int)
		_, ok := denoms[i].SetString(d, 10)
		if !ok {
			cobra.CheckErr("invalid input " + d)
		}
	}

	for r := range lib.CFracConvergents(a0, denoms) {
		fmt.Println(r)
	}
}

// FIXME: should support an initial block of non-periodic denominators (will need flags)
// convergentsCmd represents the convergents command
var convergentsCmd = &cobra.Command{
	Use:   "convergents N N [N ...]",
	Short: "Compute convergents of a periodic continued fraction",
	Long: `Compute convergents of a periodic continued fraction.

The first number given is the integer part. The following numbers give the repetend of the continued fraction.

This will output convergents infinitely. Try piping to head to only output a certain number of convergents, like this:
mathtools convergents 3 2 6 | head -n 5`,
	Args: cobra.MinimumNArgs(2),
	Run:  convergents,
}

func init() {
	rootCmd.AddCommand(convergentsCmd)

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

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

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