Kwadratic formula

[BURNY26]

Hi Im quite new to java and programming in general and I was hoping on getting some help with this piece of code.

class kwadratic {
public static void main(String []args){
for (double xxx=-1000; xxx<1000;xxx++){
double equation = xxx*xxx*3-8*xxx+4;
}
if (equation ==0){
System.out.println(xxx);
}
}
}

Im using Netbeans ...if it matters.

[JosAH]

That way you'll only find one root (2.0) if you're lucky; the other root (2/3) can not be found that way. Why don't you apply the close form formula (-b+-sqrt(b*b-4*a*c))/(2*a).

kind regards,

Jos

[BURNY26]

Well I wanted to find the solution without the formula to make it as basic as possible.

[BURNY26]

Is there any way of letting the xxx increment by ..lets say 0.01 instead of 1 ?

[JosAH]

Sure, add 0.01 to variable xxx each time through the loop:

for (double xxx= -1000; x < 1000; x+= 0.01)
    // ...

... but you still won't find the other root (2/3) that way.

kind regards,

Jos

[BURNY26]

Sweet ,but i still get an error :

[noobplus]

hi,
a variable cannot be accessed outside a block
also, every instance of the variable "equation" should be checked, but u're checking it only once after the end of the loop

regards
dhilip

[BURNY26]

Uhm , in nooblanguage please. Or most preferably in code form ???

[JosAH]

Uhm , in nooblanguage please. Or most preferably in code form ???

Put lines #6 and #7 before line #5.

kind regards,

Jos

[BURNY26]

cheers ,case dismissed

[JosAH]

So you're happy with this? Your program only finds solutions to your quadratic formula if the root is -1000+i*0.01. An ordinary quadratic formula isn't too difficult to implement ... it's not like a Jenkins-Traub method that works on arbitrary polynomials ...

kind regards,

Jos

[noobplus]

Sure, add 0.01 to variable xxx each time through the loop:

for (double xxx= -1000; x < 1000; x+= 0.01)
    // ...

Hi,

adding "0.01" to "double xxx=0" gives us approximate double values, not exact increment
for example,

for(int xxx=0;xxx<1;xxx+=0.01)
  {
    System.out.println(xxx);
  }

gives output
(first 15 output values..)

0.0
0.01
0.02
0.03
0.04
0.05
0.060000000000000005 //this is non-exact
0.07
0.08
0.09
0.09999999999999999//non-exact
0.10999999999999999//non-exact
0.11999999999999998//non-exact
0.12999999999999998//non-exact
0.13999999999999999//non-exact

this is because of rounding errors
hence even "2.0" may not be displayed
I learnt it at Java theory and practice: Where's your point?

regards
dhilip

[JosAH]

Of course you haven't read my original reply:

That way you'll only find one root (2.0) if you're lucky; the other root (2/3) can not be found that way.

Bold faced font added for clarity.

Jos

[noobplus]

Of course you haven't read my original reply:



Bold faced font added for clarity.

Jos

ok boss

[noobplus]

Of course you haven't read my original reply:



Bold faced font added for clarity.

Jos

/**
*@author:dhilipkumar(noobplus)
 */

public class kwadratic {
	static double equation;
	static double incrementedvalue;
	static double repeatchecker=-1;
	
	public static void main(String []args){
		
		
		


		
		for(int x=0;x<11;x++)
		{
			
		
		for(int i=1;i<11;i++)
		{
			for(int j=0;j<10;j++)
					{
					if(j<i)
					{
			incrementedvalue=(x+(double)j/(double)i);
			
			equation = (incrementedvalue*incrementedvalue*3)-(8*incrementedvalue)+4;
			
			if ((equation==0) && (incrementedvalue!=repeatchecker))
			{
			    
				System.out.println(incrementedvalue);
				repeatchecker=incrementedvalue;
			}
					}
					}
			
		}
		
		}
		
		
		
		}
}

output:

0.6666666666666666
2.0

we don't need to use "xxx+=0.01"


regards
dhilip

[JosAH]

we don't need to use "xxx+=0.01"

We don't need any iterations at all.

Jos

[noobplus]

We don't need any iterations at all.

Jos

and how?

dhilip

[JosAH]

and how?

dhilip

So you still haven't read this thread ...

Jos

[KevinWorkman]

"Kwadratic" is my new favorite word.

[noobplus]

So you still haven't read this thread ...

Jos

yep..basic quadratic formula .. yep..

Well I wanted to find the solution without the formula to make it as basic as possible.

maybe he wanted to become a loop-master

regards
dhilip