Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > Java > Precision problem with double

Reply
Thread Tools

Precision problem with double

 
 
Cyprien
Guest
Posts: n/a
 
      06-07-2008
Hi everyone,

I am a Java beginner, and I am trying to create a very simple binary
tree.
Each node has a value, the left child has the same value + an
increment, the right child has the same value - the same increment.
I try to recursively create the tree, but I have precision problems.

My "main" node has a value of 10, the increment is 0.1, tree depth is
4
So i want a tree that goes like this :
depth 1 : 10
depth 2 : 0.9 / 10.1
depth 3 : 0.8 / 10 / 10 / 10.2
depth 4 : 0.7 / 0.9 / 0.9 / 10.1 / 0.9 / 10.1 / 10.1 / 10.3

But at depth 4 when I try to print the value I get 9.700000000000001
instead of 9.7, and 10.299999999999999 instead of 10.3
And things get worse when the depth increase.
All the values and increment are stored in double (native type).

Is it normal? How can I avoid this problem?
Thanks a lot,
Tom.

[main class]
double increment = 0.1;
double startValue = 10;
int maxDepth = 4;
Tree myTree = new Tree(startValue, 1);
myTree.recursivelyCreateChildren(increment, maxDepth);

[Tree.java]
public int depth;
public double value;
public Tree leftChild;
public Tree rightChild;

Tree(double value, int depth){
this.value=value;
this.depth=depth;
System.out.println("node of depth " + depth + " created, value = " +
value);
}

public void createChildren(double increment){
rightChild = new Tree(value - increment, depth+1);
leftChild = new Tree(value + increment, depth+1);
}

public void recursivelyCreateChildren(double increment, int maxDepth)
{
if (depth < maxDepth){
createChildren(increment);
leftChild.recursivelyCreateChildren(increment, maxDepth);
rightChild.recursivelyCreateChildren(increment, maxDepth);
}
}

 
Reply With Quote
 
 
 
 
Patricia Shanahan
Guest
Posts: n/a
 
      06-07-2008
Cyprien wrote:
> Hi everyone,
>
> I am a Java beginner, and I am trying to create a very simple binary
> tree.
> Each node has a value, the left child has the same value + an
> increment, the right child has the same value - the same increment.
> I try to recursively create the tree, but I have precision problems.
>
> My "main" node has a value of 10, the increment is 0.1, tree depth is
> 4
> So i want a tree that goes like this :
> depth 1 : 10
> depth 2 : 0.9 / 10.1
> depth 3 : 0.8 / 10 / 10 / 10.2
> depth 4 : 0.7 / 0.9 / 0.9 / 10.1 / 0.9 / 10.1 / 10.1 / 10.3
>
> But at depth 4 when I try to print the value I get 9.700000000000001
> instead of 9.7, and 10.299999999999999 instead of 10.3
> And things get worse when the depth increase.
> All the values and increment are stored in double (native type).
>
> Is it normal? How can I avoid this problem?

....

This is normal, but you can avoid it in this situation either by using
BigDecimal, or by making your increment an integer multiple of a power
of two.

double is a binary type. It is very efficient at fairly accurate
approximate representation of a wide range of magnitudes, but gives no
preference to numbers that are exact, short, decimal fractions. In
particular, 0.1 is not exactly representable in double. On the other
hand, small integers and 1/8 are exactly representable, so you would get
exact results if you used 1/8 as increment.

BigDecimal is decimal based, and can exactly represent any integer, 0.1,
and any sum of those numbers.

Patricia
 
Reply With Quote
 
 
 
 
Roedy Green
Guest
Posts: n/a
 
      06-07-2008
On Sat, 7 Jun 2008 05:10:59 -0700 (PDT), Cyprien
<(E-Mail Removed)> wrote, quoted or indirectly quoted
someone who said :

>
>But at depth 4 when I try to print the value I get 9.700000000000001
>instead of 9.7, and 10.299999999999999 instead of 10.3


see http:://mindprod.com/jgloss/floatingpoint.html
--

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
 
Reply With Quote
 
Cyprien
Guest
Posts: n/a
 
      06-07-2008
Thanks a lot guys.
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Java double precision info@censnet.it Java 5 06-10-2009 11:10 AM
problem with double's precision towers@email.arizona.edu C++ 5 10-11-2005 05:51 AM
cannot convert parameter from 'double (double)' to 'double (__cdecl *)(double)' error Sydex C++ 12 02-17-2005 06:30 PM
Bug in double precision computing? Daniel Geisenhoff ASP .Net 1 07-29-2004 01:58 PM
high precision Math with 'double' (underflow problem) Wolfgang Java 4 02-24-2004 03:41 AM



Advertisments