107 lines
3.2 KiB
Go
107 lines
3.2 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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"strconv"
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"github.com/spf13/cobra"
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"scm.dairydemon.net/filifa/mathtools/lib"
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)
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var firstKind bool
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var secondKind bool
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var stirlingTop string
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var stirlingBottom string
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var stirlingUnsigned bool
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func stirling(cmd *cobra.Command, args []string) {
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n, err := strconv.Atoi(stirlingTop)
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if err != nil {
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cobra.CheckErr("invalid input " + stirlingTop)
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}
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k, err := strconv.Atoi(stirlingBottom)
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if err != nil {
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cobra.CheckErr("invalid input " + stirlingBottom)
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}
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var result *big.Int
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if firstKind {
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result = lib.Stirling1(n, k)
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} else if secondKind {
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result = lib.Stirling2(n, k)
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}
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if stirlingUnsigned {
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result.Abs(result)
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}
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fmt.Println(result)
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}
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// stirlingCmd represents the stirling command
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var stirlingCmd = &cobra.Command{
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Use: "stirling [-1|-2] -n N -k N",
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Short: "Compute the Stirling numbers",
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Long: `Compute the Stirling numbers.
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The Stirling numbers of the first kind give the coefficients in the expansion of the falling factorial. For example,
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x(x-1)(x-2) = x^3 - 3x^2 + 2x
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Consequently, s(3,1) = 2, s(3,2) = -3, and s(3,3) = 3.
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The Stirling numbers of the second kind count the number of ways to partition a set of n objects into k non-empty subsets. For example, there are 7 ways to partition a set of 4 objects into 2 non-empty subsets:
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{1} {2,3,4}
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{2} {1,3,4}
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{3} {1,2,4}
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{4} {1,2,3}
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{1,2} {3,4}
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{1,3} {2,4}
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{1,4} {2,3}
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Therefore S(4,2) = 7.`,
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Run: stirling,
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}
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func init() {
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rootCmd.AddCommand(stirlingCmd)
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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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// stirlingCmd.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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// stirlingCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
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stirlingCmd.Flags().BoolVarP(&firstKind, "first", "1", false, "Compute Stirling numbers of the first kind")
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stirlingCmd.Flags().BoolVarP(&secondKind, "second", "2", false, "Compute Stirling numbers of the second kind")
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stirlingCmd.MarkFlagsMutuallyExclusive("first", "second")
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stirlingCmd.MarkFlagsOneRequired("first", "second")
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stirlingCmd.Flags().StringVarP(&stirlingTop, "n", "n", "", "n")
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stirlingCmd.Flags().StringVarP(&stirlingBottom, "k", "k", "", "k")
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stirlingCmd.MarkFlagRequired("n")
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stirlingCmd.MarkFlagRequired("k")
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stirlingCmd.Flags().BoolVar(&stirlingUnsigned, "unsigned", false, "output the absolute value of the number (only relevant for first kind)")
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}
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