swift算法手记-7

@IBAction func compute(sender: AnyObject) {
//  19*x^7-31*x^5+16*x^2+7*x-90=0
//  newton迭代法求一元方程的解,最大求解范围[-100000,100000]

mytitle.stringValue="19*x^7-31*x^5+16*x^2+7*x-90=0"
let trycount = 120
var accuracy: Double = 1e-15
var answer: Double?=nil

// 估计解范围
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
}
else if leftres==0{
answer=leftbound
break
}
else if rightres==0{
answer=rightbound
break
}
}
if (leftbound==nil || rightbound==nil){
return
}
var center=leftbound!+(rightbound!-leftbound!)/2
let centres:Double=comresult(center)
if  centres==0 {
answer=center
}

if centres*comresult(rightbound!)<0{
leftbound=center
}
else if centres*comresult(leftbound!)<0{
rightbound=center
}

if answer==nil{
//计算方程的解
var p0=leftbound!+(rightbound!-leftbound!)/2
var p:Double
for i in 1...trycount{

p = newtoncompresult(p0)
if abs(p-p0) < accuracy {
answer=p0
break
}
p0=p
}
}
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))
}
}

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http://blog.csdn.net/myhaspl/