How do I make a mathematical function f(x) for any generic f?

Question

I tried searching for it via google and here but I'm not finding questions to what I mean (search engines don't understand the context by which I mean function).

Essentially I want to do the following

double f(String function, double a){
    return function.Function(a);
}

What would happen is the string function is of the form "x^2+2" it would likely be converted somehow to "x.pow(2) + 2" and then x is replaced by a and the result of the function is returned.

Is there any Java class or method that does what I said (or simple way to do it)? Or any code from another source that does what I said or a variant.

I don't have to code what I said, I just need f(x) to solve root finding problems for any function string passed as input. I thought Java would have such a method somewhere but I can't find it.

This isn't a part of the core of Java. You want a library that will parse your string and evaluate it. Search for terms like "parser" or "equation evaluator". — Lee Meador, Oct 10 '13 at 16:27
take a look at this [library project](http://sourceforge.net/projects/jep/) — Eugen Halca, Oct 10 '13 at 16:28

score 1 · Answer 1 · answered Oct 10 '13 at 16:30

So, in Java you have an essential problem because you cannot directly convert a String to a mathematical expression. Your options are as follows:

Search for a library that can convert a particularly formatted string to a mathematical expression.
Parse the string yourself. String parsing is difficult and error prone, and the Java around this would be difficult.
Use Scala, which would allow you to directly compose functions to pass into your function, rather than trying to do the expensive conversion from a human-readable string to a machine-interpretable function. Note that Scala is interoperable with Java, but has a bit of a learning curve. Other functional languages can handle this as well, but may lack interoperability.

How do I make a mathematical function f(x) for any generic f?

1 Answers1