我有一个数值求解函数(Double => Double
),我试图变得聪明并使用Numeric[T]
来保持两种数字分开。
这并不容易。剩下的问题是:
Numeric[T]
只有加号,减号等操作符。 implicit evidence$1: Numeric[Double]
函数(参见下面的编译器输出)理想情况下,我想说," A
和B
都是Double
,但请告诉我我是否将它们相互混合了#34;
以下是代码:
import scala.annotation.tailrec
class Sweep[A: Numeric, B: Numeric]( fDiff: A => B, initialSeed: A, initialStep: A, bEps: B )
{
val anum= evidence$1
val bnum= evidence$2
assert( anum.signum(initialStep) > 0 )
assert( bnum.lt( fDiff(initialSeed), fDiff( anum.plus(initialSeed,initialStep) )) ) // check that it's an increasing function
@tailrec
private def sweep( seed: A, step: A ): A = {
val bDiff= fDiff(seed)
if ( bnum.lt( bnum.abs(bDiff), bEps) ) { // done
seed
} else if ( bnum.signum(bDiff) != anum.signum(step) ) {
sweep( anum.plus(seed,step), step ) // continue, same step and direction ('bDiff' should go smaller)
} else {
val newStep = anum.toDouble(step) / -2.0
sweep( anum.minus(seed,newStep), newStep ) // reverse, smaller step
}
}
// Make sure we take the initial step in the right direction
//
private lazy val stepSign= -bnum.signum( fDiff(initialSeed) )
def apply: A = sweep( initialSeed, stepSign * initialStep )
}
object TestX extends App {
val t= new Sweep( (a: Double) => (a*a)-2, 1.0, 0.5, 1e-3 )()
println( t, math.sqrt(2.0) )
}
我已经尝试使用较旧的(implicit anum: Numeric[A])
参数,但无法使用两个(A
和B
)。
这是编译器所说的内容(Scala 2.9):
fsc -deprecation -d out-make -unchecked src/xxx.scala
src/xxx.scala:25: error: type mismatch;
found : newStep.type (with underlying type Double)
required: A
sweep( anum.minus(seed,newStep), newStep ) // reverse, smaller step
^
src/xxx.scala:33: error: overloaded method value * with alternatives:
(x: Double)Double <and>
(x: Float)Float <and>
(x: Long)Long <and>
(x: Int)Int <and>
(x: Char)Int <and>
(x: Short)Int <and>
(x: Byte)Int
cannot be applied to (A)
def apply: A = sweep( initialSeed, stepSign * initialStep )
^
src/xxx.scala:38: error: not enough arguments for constructor Sweep: (implicit evidence$1: Numeric[Double], implicit evidence$2: Numeric[Double])Sweep[Double,Double].
Unspecified value parameters evidence$1, evidence$2.
val t= new Sweep( (a: Double) => (a*a)-2, 1.0, 0.5, 1e-3 )()
^
three errors found
感谢任何想法。
答案 0 :(得分:3)
您希望使用Fractional
代替Numeric
。以下内容为我编译:
import scala.annotation.tailrec
import math.Fractional.Implicits._
import Ordering.Implicits._
class Sweep[A: Fractional, B: Fractional](fDiff: A => B, initialSeed: A, initialStep: A, bEps: B) {
val aFractional = implicitly[Fractional[A]]
assert(initialStep.signum > 0)
assert(fDiff(initialSeed) < fDiff(initialSeed + initialStep))
@tailrec
private def sweep(seed: A, step: A): A = {
val bDiff = fDiff(seed)
if (bDiff.abs < bEps) {
seed
} else if (bDiff.signum != step.signum) {
sweep(seed + step, step)
} else {
val one = aFractional.one
val newStep = step / aFractional.fromInt(-2)
sweep(seed - newStep, newStep)
}
}
private lazy val stepSign = aFractional.fromInt(-fDiff(initialSeed).signum)
def apply: A = sweep(initialSeed, stepSign * initialStep)
}
val sweep = new Sweep((a: Double) => (a*a)-2, 1.0, 0.5, 1e-3)
println(sweep.apply, math.sqrt(2.0))
请注意,要在-2.0
类型中获取A
之类的内容,您需要从Fractional.one
手动汇总它们或使用Fractional.fromInt
。
值得指出的另一件事是使用math.Fractional.Implicits
和Ordering.Implicits
,这将允许您使用普通的数学语法(+,&lt;,/等),而不是像{一样调用函数{1}}和plus
。
答案 1 :(得分:0)
如果您希望编译器告诉您何时类型参数A
和B
不相同,只需使用一个类型参数:
class Sweep[A: Numeric]( fDiff: A => A, initialSeed: A, initialStep: A, bEps: A )
答案 2 :(得分:0)
问题似乎是你在这里使用Double
......
val newStep = anum.toDouble(step) / -2.0
...虽然您想使用Numeric
并在下一行实际使用它。
对于除法,请查看Numeric
的子类型Integral
和Fractional
。
编译器找不到隐式证据,因为你明确地传递了无:
new Sweep((a: Double) => (a*a)-2, 1.0, 0.5, 1e-3)()
删除显式空参数列表修复了:
new Sweep((a: Double) => (a*a)-2, 1.0, 0.5, 1e-3)
我不确定不要混合A
和B
的要求,因为您已经在代码的多个位置执行此操作。
我不确定这是你想要的,但以下代码有效:
import scala.annotation.tailrec
class Sweep[A: Fractional](fDiff: A => A, initialSeed: A, initialStep: A, bEps: A) {
val num = implicitly[Fractional[A]]
assert(num.signum(initialStep) > 0)
assert(num.lt(fDiff(initialSeed), fDiff(num.plus(initialSeed, initialStep)))) // check that it's an increasing function
@tailrec
private def sweep(seed: A, step: A): A = {
val bDiff = fDiff(seed)
if (num.lt(num.abs(bDiff), bEps)) { // done
seed
} else if (num.signum(bDiff) != num.signum(step)) {
sweeimport scala.annotation.tailrec
class Sweep[A: Fractional](fDiff: A => A, initialSeed: A, initialStep: A, bEps: A) {
val num = implicitly[Fractional[A]]
assert(num.signum(initialStep) > 0)
assert(num.lt(fDiff(initialSeed), fDiff(num.plus(initialSeed, initialStep)))) // check that it's an increasing function
@tailrec
private def sweep(seed: A, step: A): A = {
val bDiff = fDiff(seed)
if (num.lt(num.abs(bDiff), bEps)) { // done
seed
} else if (num.signum(bDiff) != num.signum(step)) {
sweep(num.plus(seed, step), step) // continue, same step and direction ('bDiff' should go smaller)
} else {
val newStep = num.div(step, num.fromInt(-2))
sweep(num.minus(seed, newStep), newStep) // reverse, smaller step
}
}
// Make sure we take the initial step in the right direction
private lazy val stepSign = -num.signum(fDiff(initialSeed))
def apply: A = sweep(initialSeed, num.times(num.fromInt(stepSign), initialStep))
}
object TestX extends App {
val t = new Sweep((a: Double) => (a * a) - 2, 1.0, 0.5, 1e-3)
println(t, math.sqrt(2.0))
}
p(num.plus(seed, step), step) // continue, same step and direction ('bDiff' should go smaller)
} else {
val newStep = num.div(step, num.fromInt(-2))
sweep(num.minus(seed, newStep), newStep) // reverse, smaller step
}
}
// Make sure we take the initial step in the right direction
private lazy val stepSign = -num.signum(fDiff(initialSeed))
def apply: A = sweep(initialSeed, num.times(num.fromInt(stepSign), initialStep))
}
object TestX extends App {
val t = new Sweep((a: Double) => (a * a) - 2, 1.0, 0.5, 1e-3)
println(t, math.sqrt(2.0))
}