public static void main(String[] args) { // TODO code application logic here String ki = "x2 + 4x  12"; double y = computeValue(ki, 0, x); x=2; } private double computeValue(String rawNumber, double x) { String current; int index1 = rawNumber.indexOf(43); // finding the position of + in the string int index2 = rawNumber.indexOf(45,1); // finding the position of  in the string after 1 int startIndex=0; int endIndex; boolean hasSign= ( index1 != 1 )  (index2 != 1); boolean isVariable=false; double number=0; double coeff, power; int whereX=1; coeff = power = 1; if(rawNumber.charAt(0) == '') // if the first char is minus, make the coefficient negative { coeff=coeff; startIndex=1; } if( hasSign) { if( index1 == 1 ) endIndex = index2; else if(index2 == 1 ) endIndex = index1; else endIndex = Math.min(index1, index2)  1; } else endIndex = rawNumber.length() ; current=rawNumber.substring( startIndex, endIndex ).trim(); whereX=current.indexOf("x"); if(whereX != 1 ) //change the value of the coeff and power only if there is a x symbol { if( whereX > 0) coeff= coeff * Double.parseDouble( current.substring(0, whereX) ); if( whereX + 1 < current.length()) power=power * Double.parseDouble( current.substring(whereX+1 ) ); } else //otherwise, parse the whole string ( a constant number into the coefficient) { coeff = coeff * Double.parseDouble( current); power=0; } //note that if x^0 = 1 number= coeff * ( Math.pow(x, power) ); if( hasSign ) { if( rawNumber.charAt(endIndex) == '+' ) { number = number + isolateArg(rawNumber.substring(endIndex + 1), 0, x); } else { number = number  isolateArg(rawNumber.substring(index1 + 1), 0, x); } } return number; }
finding the numeric value of a polynomial
Page 1 of 14 Replies  500 Views  Last Post: 01 December 2011  09:24 AM
#1
finding the numeric value of a polynomial
Posted 30 November 2011  05:35 AM
I'm trying to compute the value of a polynomial from a string formula, but I can't get this one equation to return the right value and I suspect it's because it doesn't process the  sign properly ( the run is correct for x2+4x +12). In this code x2 means x squared so a power directly follows the x symbol. Please excuse the lack of comments, I'm a relatively new at programming and using forums.. What I basically try to do is isolate each term without the +/ signs and find their value before making recursive calls to the same compute function. PLease, help!
Replies To: finding the numeric value of a polynomial
#2
Re: finding the numeric value of a polynomial
Posted 30 November 2011  07:36 AM
Do you have to do this using Strings? Using classes and objects provides a much cleaner way of doing things. This should give you a better idea of what I'm talking about, and a good starting point. Now you can simply add Term objects to the Polynomial object.
class Term{ private int coefficient, exponent; //other code public double evaluate(){ return Math.pow(coefficient, exponent); } } class Polynomial{ private Term[] terms; //other code public double evaluate(){ double sum = 0; for(Term t:terms) sum += t.evaluate(); return sum; } }
#3
Re: finding the numeric value of a polynomial
Posted 30 November 2011  08:34 PM
My bad.. indexOf('+') and indexOf('') would have been cleaner
This post has been edited by pbl: 30 November 2011  08:39 PM
#4
Re: finding the numeric value of a polynomial
Posted 01 December 2011  06:40 AM
I guess I am really wanting to make use of srings for this because I want to create a user friendly program, macosxnerd101. You did however raise the fact that I could encapsulate more and probably find an easier way to compute the numbers using a termby term basis.
#5
Re: finding the numeric value of a polynomial
Posted 01 December 2011  09:24 AM
I would do this:
Replace all  signs with + so you can split() on the + signs and keep the  terms.
Parse through the array returned by the split() method to parse each individual term into Term objects.
Add those Term objects into the Polynomial object.
Replace all  signs with + so you can split() on the + signs and keep the  terms.
Parse through the array returned by the split() method to parse each individual term into Term objects.
Add those Term objects into the Polynomial object.
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