90 lines
2.4 KiB
Go
90 lines
2.4 KiB
Go
/*
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Copyright © 2025 filifa
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package cmd
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import (
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"fmt"
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"math/big"
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"github.com/spf13/cobra"
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"scm.dairydemon.net/filifa/mathtools/internal/lib"
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)
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var pellCoeff string
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func pell(cmd *cobra.Command, args []string) {
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d, ok := new(big.Int).SetString(pellCoeff, 10)
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if !ok {
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cobra.CheckErr("invalid input " + args[0])
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}
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a0 := new(big.Int).Sqrt(d)
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repetend, err := lib.SqrtRepetend(d)
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if err != nil {
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cobra.CheckErr(pellCoeff + " is a perfect square")
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}
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r := len(repetend)
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var period int
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if r%2 == 0 {
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period = r
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} else {
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period = 2 * r
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}
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ch := lib.CFracConvergents(a0, repetend)
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// TODO: consider breaking after finding the fundamental solution and using the recurrence relation to find the following solutions
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for i := 1; true; i = (i + 1) % period {
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r := <-ch
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if i == period-1 {
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fmt.Println(r.Num(), r.Denom())
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}
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}
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}
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// pellCmd represents the pell command
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var pellCmd = &cobra.Command{
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Use: "pell -d N",
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Short: "Find solutions to a Pell equation",
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Long: `Find integer solutions to a Pell equation x^2 - dy^2 = 1.
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This will output solutions infinitely. Try piping to head to only output a certain number of solutions, like this:
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mathtools pell -d 12 | head -n 5`,
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Run: pell,
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}
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func init() {
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rootCmd.AddCommand(pellCmd)
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// Here you will define your flags and configuration settings.
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// Cobra supports Persistent Flags which will work for this command
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// and all subcommands, e.g.:
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// pellCmd.PersistentFlags().String("foo", "", "A help for foo")
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// Cobra supports local flags which will only run when this command
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// is called directly, e.g.:
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// pellCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
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pellCmd.Flags().StringVarP(&pellCoeff, "coefficient", "d", "", "coefficient")
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pellCmd.MarkFlagRequired("coefficient")
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// TODO: add support for generalized Pell equations
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}
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