alice-teacher Possible Problem with Alice 3.3

[Wanda Dann]

Please forgive me for plugging the new book... but for purposes of providing
and Alice example of the "rounding error" that occurs in floating point 
computations,
see Chapter 16, sections 16.7.2 and 16.7.3, of the new /Alice 3 to Java/ 
textbook.

Wanda

On 6/4/2017 3:19 PM, Michael L Owen wrote:
>
> Hi Don- Nope, You got it right. It just threw me off a bit when I was 
> originally using 0.2 as the increment value and getting the long 
> strings with 3DText. As Terri mentioned, there is always a way to get 
> around a binary kludge like this, and probably good to inform students 
> that computers aren't always perfect.
>
> Including a patched version that works a little better.
>
>
> Mike
>
> ------------------------------------------------------------------------
> *From:* alice-teachers 
> <alice-teachers-bounces+mrgrog=outlook.com at lists.andrew.cmu.edu> on 
> behalf of Donald Slater <djslater107 at mac.com>
> *Sent:* Sunday, June 4, 2017 8:52 AM
> *To:* Alice Teachers
> *Subject:* Re: alice-teacher Possible Problem with Alice 3.3
> Michael,
> If I understand what you are saying correctly, and if I am seeing what 
> you are seeing when I run your program, you are seeing the results of 
> floating point addition (in Java and other programming languages). 
> (See the Rounding Error section in the following document: 
> https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html)
> What Every Computer Scientist Should Know About Floating ... 
> <https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html>
> docs.oracle.com
> Abstract. Floating-point arithmetic is considered an esoteric subject 
> by many people. This is rather surprising because floating-point is 
> ubiquitous in computer systems.
>
>
>
> When I run Java equivalent code, as in:
>
> double counter = 0.0;
>         while (counter < 2.0) {
>             counter += 0.1;
>             System.out.println("counter: " + counter);
>         }
>
> I get the following output:
>
>     counter: 0.1
>     counter: 0.2
>     counter: 0.30000000000000004
>     counter: 0.4
>     counter: 0.5
>     counter: 0.6
>     counter: 0.7
>     counter: 0.7999999999999999
>     counter: 0.8999999999999999
>     counter: 0.9999999999999999
>     counter: 1.0999999999999999
>     counter: 1.2
>     counter: 1.3
>     counter: 1.4000000000000001
>     counter: 1.5000000000000002
>     counter: 1.6000000000000003
>     counter: 1.7000000000000004
>     counter: 1.8000000000000005
>     counter: 1.9000000000000006
>     counter: 2.0000000000000004
>
> If you make your counter a WholeNumber variable, which is our typical 
> implementation, which might make sense as you are using a 1 second 
> delay between each update, your code will work as you expect.
>
> Although this is not a bug, it may suggest that sometime Alice 
> implement a decimal precision option that mimics the DecimalFormat 
> class of Java… See the following Java example and output
>
> double counter = 0.0;
>         while (counter < 2.0) {
>             counter += 0.1;
> *DecimalFormat df = new DecimalFormat("#.##");*
>             System.out.println("counter: " + df.format(counter));
>         }
>
> Output:
>
>     counter: 0.1
>     counter: 0.2
>     counter: 0.3
>     counter: 0.4
>     counter: 0.5
>     counter: 0.6
>     counter: 0.7
>     counter: 0.8
>     counter: 0.9
>     counter: 1
>     counter: 1.1
>     counter: 1.2
>     counter: 1.3
>     counter: 1.4
>     counter: 1.5
>     counter: 1.6
>     counter: 1.7
>     counter: 1.8
>     counter: 1.9
>     counter: 2
>
>
> This is probably not something that will happen soon, however.
>
> I apologize if I have misunderstood you in some way.
>
> Thank you,
> Don Slater
>
>
>> On Jun 3, 2017, at 2:39 PM, Michael L Owen <mrgrog at outlook.com 
>> <mailto:mrgrog at outlook.com>> wrote:
>>
>> Hi All- I was looking at a post recently that addressed adding a 
>> timer loop to a program that would display the timer while counting 
>> up to the finish.
>> I decided to try few options, but into a problem with the display 
>> almost immediately. I'm running the 64-bit Alice 3.3.
>> On my machine the number displayed appears to be encountering a 
>> rounding error of some sort that causes the number to be expanded the 
>> maximum.
>>
>> Maybe a Bug?
>> Mike Owen
>>
>> <TimerExample.a3p>_______________________________________________
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>
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