swift算法手记-5

//
//  ViewController.swift
//  learn5
//
//  Created by myhaspl on 16/1/23.
//  Copyright (c) 2016年 myhaspl. All rights reserved.
//

import Cocoa
import Foundation

class ViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override var representedObject: AnyObject? {
        didSet {
        // Update the view, if already loaded.
        }

    }
    private func comresult(inputnum:Double)->Double{
        //  5*x^7-3*x^5+16*x^2+7*x+90=0
        let myresult:Double = 5 * pow(inputnum,7) - 3 * pow(inputnum,5) + 16 * pow(inputnum,2) + 7 * inputnum + 90
        return myresult
    }
    @IBOutlet weak var result: NSTextField!

    @IBAction func compute(sender: AnyObject){
//  5*x^7-3*x^5+16*x^2+7*x+90=0
//  二分法求一元方程的解,最大求解范围[-100000,100000]
      let trycount = 80
      var accuracy: Double = 0.00000000000001
      var answer: Double?
=nil
     // 预计解范围
      var leftbound:Double?=nil
      var rightbound:Double?=nil
        for var bound:Double=1;bound<10000000;bound*=10{
          let leftres=comresult(-bound)
          let rightres=comresult(bound)
          if  (leftres*rightres) < 0 {
              leftbound = (-bound)
              rightbound = bound
              break
          }
      }
      if (leftbound==nil || rightbound==nil){
          return 
      }
      //计算方程的解
          for i in 1...trycount{
                result.stringValue=String(i)
                let center=leftbound!+(rightbound!-leftbound!)/2
                let leftres:Double=comresult(leftbound!)
                let rightres:Double=comresult(rightbound!)
                let centres:Double=comresult(center)
                if centres==0 {
                    answer=center
                    break
                }
                else if abs(rightbound!-leftbound!) < accuracy {
                    answer=leftbound!
                    break                   
                }
                else if leftres*centres<0{
                    rightbound=center
                }
                else if rightres*centres<0{
                    leftbound=center
                }  
            }         

      if let ans=answer{
        //方程有解
         result.stringValue="解："+String(stringInterpolationSegment: ans)+"   "
         result.stringValue += "解代入方程的值："+String(stringInterpolationSegment:comresult(ans))
      }     
    }
}