java + negative exponents

champ · 08-08-2004, 05:34 AM

Hi

Im trying to implement a algorithm in java using BigInteger class.
The problem is that I have to use negative exponents, but that doesn't work.
I have a value V which i want to raise to the power of -1. The BigInteger class has a method pow() which I can use, but it will raise an exception if I use a neg. exp.

How can I solve this?

max_sipos · 08-08-2004, 06:39 AM

Umm, I don't know anything about the BigInteger class. But if it is an integer, raising it to the power of -1 is equivalent to dividing 1 by the number which is bound to be a decimal number, not an integer.. The best thing it would do was give you a 0 as a result...

champ · 08-11-2004, 12:07 AM

I found the solution....

I use modular inversion. B = A^-1. B is the modular multiplicative inverse of A. And BigInteger class has a method called modInverse().

Code:

  BigInteger b = a.modInverse(modulusUsedInAlgorithm)

Since im using modular, the fraction will be lost. So it can be represented as a Integer