CODEWITHSUNDEEP
javaandroid
user3198094
user3198094

Reputation: 31

Convert a string into mathematical equation?

I'm a beginner. I want to convert a string into a mathematical equation in order to be the input of my graphic calculator for example:

cos(x+1)+ ln(x)

so we will convert it to 

double x = -10;
for (int i=0; i<100; i++) { 
double y=Math.cos(x+1)+Math.log(x)
x=x+0.5         
}

so I want to know a method of converting y

Thank You

Upvotes: 2

Views: 3868

Answers (5)

kleineg
kleineg

Reputation: 491

I did that exact thing using NCalc. I passed in the user's string expression, replaced the variables with the values I am evaluating at, then using the Evaluate method and parsing to a double.

private double Function(double t, double y)
    {
        NCalc.Expression expression = new NCalc.Expression(this.Expression);
        expression.Parameters["t"] = t;
        expression.Parameters["y"] = y;

        double value;

        double.TryParse(expression.Evaluate().ToString(), out value);

        return value;        
    }

For example, given the inputs t = .5 and y = 1 and the expression "4*y + Tan(2*t)", we would evaluate the string "4*1 + Tan(2*.5)" using NCalc.

It is not perfect, NCalc throws an exception if it cannot parse the user's string or it the datatypes of functions are different. I am working on polishing it.

I also asked the same question here.

Upvotes: 1

Don Kartacs
Don Kartacs

Reputation: 426

There is no "out-of-the-box" solution in java for this.

However: Obligatory answer: google -> "convert string to mathematical expression java" first few answers are pretty good (like: What's a good library for parsing mathematical expressions in java? ) Obligatory answer 2: There are quite a few libraries on the net for converting strings into math expressions, naming them would be off-topic according to the rules, so I suggest "Obligatory answer" first few hits.

Also most likely you are better off by choosing a Format you will receive, and write your own parser for that format.

Upvotes: 2

tfandango
tfandango

Reputation: 133

This is not a simple thing to do in pure Java. There are a lot of other similar questions with good answers here. Most of the solutions have to do with evaluating the expression in an interpreter or parsing the expression (there are some libraries available for this), or even shelling out. I don't know what is available in Android specifically to do this but there are tons of good answers for this in SO. Here is a good one to start with: Evaluating a math expression given in string form

Upvotes: 1

peter.petrov
peter.petrov

Reputation: 39457

You need to have a small formal grammar describing the syntax of your expression, then you need to convert your input string expression to an AST representation.

http://en.wikipedia.org/wiki/Abstract_syntax_tree

Finally you need to have a procedure to evaluate the AST for certain values of the parameters.

Upvotes: 1

Halfgaar
Halfgaar

Reputation: 772

You need to write a parser first, building a tree of your input expression. You can then use that to generate your code.

But, "I'm a beginner" doesn't go well with writing parsers :)

Upvotes: 1

Related Questions