Calculating roots with bc_math or GMP

Question

I'm having trouble calculating roots of rather large numbers using bc_math, example:

 - pow(2, 2)     // 4, power correct
 - pow(4, 0.5)   // 2, square root correct
 - bcpow(2, 2)   // 4, power correct
 - bcpow(4, 0.5)     // 1, square root INCORRECT

Does anybody knows how I can circumvent this? gmp_pow() also doesn't work.

Answer 1

I'm not a PHP programmer but looking at the manual it says you have to pass them in as strings i.e.

bcpow( '4', '0.5' )

Does that help?

Edit: The user contributed notes in the manual page confirm that it doesn't support non-integer exponents.

I did come across this discussion of a PHP N-th root algorithm after a quick search so perhaps that's what you require.

Answer 2

For future reference here it is:

• http://mgccl.com/2007/01/24/bcpows-no-fraction-exponent-limitation-and-work-around/
• http://mgccl.com/2007/01/30/new-upgrade-on-bcroot-speed-boost/