[英]Generic Linear Piecewise Lookup Table
I am looking for a generic optimized lookup object that takes a function f(x) and creates a linear piecewise approximation with configurable parameters for the range of x and the intervals of population. 我正在寻找一个通用的优化查找对象,它采用函数f(x)并创建一个线性分段近似,其中包含x的范围和总体间隔的可配置参数。
Obviously this is not hard to write, but given that it is useful for a lot of expensive functions (trig, yield, distance), I thought a generic one might already exist. 显然这并不难写,但鉴于它对很多昂贵的函数(trig,yield,distance)很有用,我认为一个通用的函数可能已经存在。 Please let me know.
请告诉我。
Another useful feature would be to serialize / deserialize the lookup table as a rather precise 100,000 point+ table can take several minutes to construct. 另一个有用的功能是序列化/反序列化查找表,因为相当精确的100,000点+表可能需要几分钟才能构建。
I don't believe anything exists in the .NET class libraries directly. 我不相信.NET类库中直接存在任何内容。 Something may exist in a third party library ( like C5 perhaps ).
第三方库中可能存在某些东西( 比如C5 )。
Creating a generic version of a function that can accept ranges is a bit tricky in C#, since there is no unifying type or interface which provides arithmetic operators. 在C#中创建可以接受范围的函数的泛型版本有点棘手,因为没有统一类型或接口提供算术运算符。 However, with some creativity, it's possible to craft something:
然而,通过一些创造力,可以制作一些东西:
// generic linear lookup class, supports any comparable type T
public class LinearLookup<T> where T : IComparable<T>
{
private readonly List<T> m_DomainValues = new List<T>();
public LinearLookup( Func<T,T> domainFunc, Func<T,T> rangeFunc,
T lowerBound, T upperBound )
{
m_DomainValues = Range( domainFunc, rangeFunc,
lowerBound, upperBound )
.ToList();
}
public T Lookup( T rangeValue )
{
// this could be improved for numeric types
var index = m_DomainValues.BinarySearch( rangeValue );
if( index < 0 )
index = (-index)-1;
return m_DomainValues[index];
}
private static IEnumerable<T> Range( Func<T,T> domainFunc,
Func<T,T> rangeFunc, T lower, T upper )
{
var rangeVal = lower;
do
{
yield return domainFunc( rangeVal );
rangeVal = rangeFunc( rangeVal );
} while( rangeVal.CompareTo( upper ) < 0 );
}
}
This class will precompute a set of domain values for the function domainFunc
over the range [lower,upper>. 此类将在[lower,upper>]范围内为函数
domainFunc
预计算一组域值。 It uses binary search for lookup - a compromise that allows any comparable type to be used - not just built in numeric types. 它使用二进制搜索进行查找 - 允许使用任何类似类型的折衷方案 - 不仅仅是以数字类型构建。 The function
rangeFunc
allows the increment to be controlled by external code. 函数
rangeFunc
允许增量由外部代码控制。 So, here's a linear lookup for Math.Sin
over the range [0,PI/2> with an increment of 0.01: 因此,这里是
Math.Sin
在[0,PI / 2>范围内的增量为0.01的线性查找:
var sinLookup = new LinearLookup( Math.Sin, x => x + 0.01d, 0, Math.PI/2 );
var lookupPI4 = sinLookup[Math.PI/4]; // fetch the value sin(π/4)
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