Raising a decimal to a power of decimal?

Question

The .net framework provides in the Math class a method for powering double. But by precision requirement I need to raise a decimal to a decimal power [ Pow(decimal a, decimal b) ]. Does the framework have such a function? Does anyone know of a library with this kind of function?

Answer 1

To solve my problem I found some expansion series, and them I had them implemented to solve the equation X^n = e^(n * ln x).

// Adjust this to modify the precision public const int ITERATIONS = 27;  // power series public static decimal DecimalExp(decimal power) {     int iteration = ITERATIONS;     decimal result = 1;      while (iteration > 0)     {         fatorial = Factorial(iteration);         result += Pow(power, iteration) / fatorial;         iteration--;     }     return result; }  // natural logarithm series public static decimal LogN(decimal number) {     decimal aux = (number - 1);     decimal result = 0;     int iteration = ITERATIONS;     while (iteration > 0)     {         result += Pow(aux, iteration) / iteration;         iteration--;     }     return result; }  // example void main(string[] args) {     decimal baseValue = 1.75M;     decimal expValue = 1/252M;     decimal result = DecimalExp(expValue * LogN(baseValue)); } 

The Pow() and Factorial() functions are simple because the power is always an int (inside de power series).

Answer 2

This should be the fastest for a positive integer Exponent and a decimal base:

// From http://www.daimi.au.dk/~ivan/FastExpproject.pdf // Left to Right Binary Exponentiation public static decimal Pow(decimal x, uint y){     decimal A = 1m;     BitArray e = new BitArray(BitConverter.GetBytes(y));     int t = e.Count;      for (int i = t-1; i >= 0; --i) {         A *= A;         if (e[i] == true) {             A *= x;         }     }     return A; }