问题
I am developing a mathematical parser which is able to evaluate String like \'5+b*sqrt(c^2)\'. I am using ANTLR for the parsing and make good progress. Now I fell over the Java class BigDecimal and thought: hey, why not thinking about precision here.
My problem is that the Java API does not provide trigonometric methods for BigDecimals like java.lang.Math. Do you know if there are any good math libraries like Apache Commons out there that deal with this problem?
The other questions is how to realize the power method so that I can calculate 4.9 ^ 1.4 with BigDecimals. Is this possible?
A book request about numerical computing is also appreciated.
回答1:
ApFloat is a library which contains arbitrary-precision approximations of trigometric functions and non-integer powers both; however, it uses its own internal representations, rather than BigDecimal and BigInteger. I haven't used it before, so I can't vouch for its correctness or performance characteristics, but the api seems fairly complete.
回答2:
BigDecimal does not provide these methods because BigDecimal models a rational number. Trigonometric functions, square roots and powers to non-integers (which I guess includes square roots) all generate irrational numbers.
These can be approximated with an arbitrary-precision number but the exact value can't be stored in a BigDecimal. It's not really what they're for. If you're approximating something anyway, you may as well just use a double.
回答3:
The big-math library provides all the standard advanced mathematical functions (pow, sqrt, log, sin, ...) for BigDecimal.
https://github.com/eobermuhlner/big-math
回答4:
Using an existing feature of Java BigDecimals, namely to allow limited precision arithmetic as described here, I recently implemented sqrt/1, exp/1, tan/1, etc.. for these number objects.
The numeric algorithms themselve use Maclaurin and Taylor series, plus appropriate range reductions to assure enough speed and breadth of the series.
Here is an example calculation, Ramanujan's Constant:
Jekejeke Prolog 2, Runtime Library 1.1.8
(c) 1985-2017, XLOG Technologies GmbH, Switzerland
?- use_module(library(stream/console)).
% 0 consults and 0 unloads in 0 ms.
Yes
?- X is mp(exp(pi*sqrt(163)), 60).
X = 0d262537412640768743.999999999999250072597198185688879353856320
The thingy was written in mixture of Prolog and Java. The speed and accuracy of it is still work in progress. The code is currently open source on GitHub.
回答5:
Pretty much the best book on Numerical Computing would be Numerical Recipes
来源：https://stackoverflow.com/questions/2173512/java-bigdecimal-trigonometric-methods