static BigNumber Logarithm(BigNumber y)
{ // y in ( -0.05-, 0.05+ ), return ln((1+y)/(1-y))
BigNumber v = (new BigNumber("1")), y2 = y * y, t = y2, z = t / (new BigNumber("3"));
for (BigNumber i = new BigNumber("3"); CompareNumber.Compare(z, new BigNumber("0")) != 0;
z = (t *= y2) / (i += new BigNumber("2")))
{
v += z;
}
return(v * y * (new BigNumber("2")));
}
//判定小于
public static bool operator <(BigNumber x1, BigNumber x2)
{
if (CompareNumber.Compare(x1, x2) == -1)
{
return(true);
}
else
{
return(false);
}
}
public static BigNumber Log(BigNumber x)
{
if (CompareNumber.Compare(x, new BigNumber("0")) == -1 || CompareNumber.Compare(x, new BigNumber("0")) == 0)
{
throw new ArgumentException("Must be positive");
}
int k = 0, l = 0;
for (; CompareNumber.Compare(x, new BigNumber("1")) == 1; k++)
{
x /= new BigNumber("10");
}
for (; CompareNumber.Compare(x, new BigNumber("0.1")) == -1; k--)
{
x *= new BigNumber("10"); // ( 0.1, 1 ]
}
for (; CompareNumber.Compare(x, new BigNumber("0.9047")) == -1; l--)
{
x *= new BigNumber("1.2217"); // [ 0.9047, 1.10527199 )
}
return(k * ln10 + l * lnr + Logarithm((x - new BigNumber("1")) / (x + new BigNumber("1"))));
}
public int CompareTo(BigNumber other)
{
return(CompareNumber.Compare(this, other));
}