factor.java

package jmathlib.toolbox.general;

import jmathlib.core.tokens.numbertokens.DoubleNumberToken;
import jmathlib.core.tokens.Token;
import jmathlib.core.tokens.OperandToken;
import jmathlib.core.functions.ExternalFunction;
import jmathlib.core.interpreter.GlobalValues;

/**External function to create a vector of the prime
factors of a number*/
public class factor extends ExternalFunction
{
	/**@param operands[0] = the number
	@return a vector containing the prime factors*/
	public OperandToken evaluate(Token[] operands, GlobalValues globals)
	{
		DoubleNumberToken result = null;

        if (getNArgIn(operands) != 1)
			throwMathLibException("factor: number of arguments != 1");
            
	    if (!(operands[0] instanceof DoubleNumberToken)) 
        	throwMathLibException("factor: first argument must be a number");
		
		double maxValue = ((DoubleNumberToken)operands[0]).getValueRe();
			
		int temp = (new Double(maxValue/2)).intValue();
		double[][] tempResults = new double[1][temp];
			
		int count = 0;
		double end = maxValue;
		double tempVal = maxValue / 2;			
		if(java.lang.Math.ceil(tempVal) == tempVal)
		{
			tempResults[0][count] = 2;
			count++;
			maxValue = tempVal;
		}
		
        for(int index = 3; index < end; index += 2)
		{
			if(isPrime(index) == 1)
			{		
				tempVal = maxValue / index;			
				if(java.lang.Math.ceil(tempVal) == tempVal)
				{
					tempResults[0][count] = index;
					count++;
					maxValue = tempVal;
				}
			}
		}

		double[][] results = new double[1][count];
			
		for(int index = 0; index < count; index++)
		{
			results[0][index] = tempResults[0][index];
		}
		result	= new DoubleNumberToken(results);			
		
        return result;
	}

	private double isPrime(double value)
	{
		double result = 0;
		
		if(value == 2)
			result = 1;
		else if((java.lang.Math.ceil(value/2) != (value/2)) && (value > 2))
		{
			result = 1;
			for(int index = 3; index < value && result != 0; index += 2)
			{
				double temp = value/index;
				if(java.lang.Math.ceil(temp) == temp)
					result = 0;
			}
		}
		
		return result;
	}
}

/*
@GROUP
general
@SYNTAX
answer=factor(values)
@DOC
Calculates all the prime factors of value.
@EXAMPLES
<programlisting>
factor(10)=[2,5]  
factor(30)=[2,3,5]
</programlisting>
@NOTES
This function will take a long time when factorising large values
@SEE
*/