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Jason is a programming language to develop BDI/cognitive agents

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package jason.functions;

import jason.JasonException;
import jason.asSemantics.DefaultArithFunction;
import jason.asSemantics.TransitionSystem;
import jason.asSyntax.ListTerm;
import jason.asSyntax.NumberTerm;
import jason.asSyntax.Term;

/**
Function: math.std_dev(L): returns the standard deviation of all values of L.

Examples:

 math.std_dev([1,2,3]): returns 1.
 math.std_dev([]): returns 0.


@author Francisco Grimaldo

@see jason.functions.Min
@see jason.functions.Max
@see jason.functions.Sum
@see jason.functions.Average

*/
public class StdDev extends DefaultArithFunction  {

    public String getName() {
        return "math.std_dev";
    }

    @Override
    public double evaluate(TransitionSystem ts, Term[] args) throws Exception {
        if (args[0].isList()) {
            double sum = 0, squareSum = 0, num;
            int    n = 0;
            for (Term t: (ListTerm)args[0])
                if (t.isNumeric()) {
                    if (t.isNumeric()) {
                        num = ((NumberTerm)t).solve();
                        sum += num;
                        n++;
                    }
                }
            double mean = sum  / n;
            for (Term t: (ListTerm)args[0])
                if (t.isNumeric()) {
                    num = ((NumberTerm)t).solve();
                    squareSum += (num - mean) * (num - mean);
                }
            return Math.sqrt( squareSum/(n - 1) );
        }
        throw new JasonException(getName()+" is not implemented for type '"+args[0]+"'.");
    }

    @Override
    public boolean checkArity(int a) {
        return a == 1;
    }
}