1. Bug in math.e?
- Posted by Thomas Jun 13, 2010
- 1533 views
When running som test with round in std/math.e i got some weird result. This was what i got round(22/7,3) = 3 I may be wrong in expecting 3.143? The following code gives the expexted result.
function ROUND(atom n, integer s = 1) atom r = n * power(10, s) + .5 r = floor(r) return r / power(10, s) end function
2. Re: Bug in math.e?
- Posted by DerekParnell (admin) Jun 13, 2010
- 1550 views
When running som test with round in std/math.e i got some weird result.
This was what i got round(22/7,3) = 3
I may be wrong in expecting 3.143?
It's not well documented but to get the result you were expecting you need to code ...
round(22/7, 1000)
The precision parameter is in terms of powers-of-ten.
| Value | Precision | Result |
|---|---|---|
| 1.2345 | 1 | 1 |
| 1.2345 | 10 | 1.2 |
| 1.2345 | 100 | 1.23 |
| 1.2345 | 1000 | 1.234 |
3. Re: Bug in math.e?
- Posted by Thomas Jun 13, 2010
- 1549 views
It's not well documented but to get the result you were expecting you need to code ... OK Thank you
4. Re: Bug in math.e?
- Posted by Anthill Nov 30, 2010
- 1325 views
Round seems to give me a problem. Is there a way to get the expected output?
atom a a = 183.4126 puts(1,to_string(round(a))) -- got 183, expected 183 puts(1,to_string(round(a,10))) -- got 183.400000000000006, expected 183.4 puts(1,to_string(round(a,100))) -- got 183.409999999999997, expected 183.42 puts(1,to_string(round(a,1000))) -- got 183.413000000000011, expected 183.413
5. Re: Bug in math.e?
- Posted by mattlewis (admin) Nov 30, 2010
- 1294 views
Round seems to give me a problem. Is there a way to get the expected output?
atom a a = 183.4126 puts(1,to_string(round(a))) -- got 183, expected 183 puts(1,to_string(round(a,10))) -- got 183.400000000000006, expected 183.4 puts(1,to_string(round(a,100))) -- got 183.409999999999997, expected 183.42 puts(1,to_string(round(a,1000))) -- got 183.413000000000011, expected 183.413
The output looks correct to me. The differences look like the rounding errors inherent in using floating point numbers.
Matt
6. Re: Bug in math.e?
- Posted by DerekParnell (admin) Nov 30, 2010
- 1278 views
Round seems to give me a problem. Is there a way to get the expected output?
atom a a = 183.4126 puts(1,to_string(round(a))) -- got 183, expected 183 puts(1,to_string(round(a,10))) -- got 183.400000000000006, expected 183.4 puts(1,to_string(round(a,100))) -- got 183.409999999999997, expected 183.42 puts(1,to_string(round(a,1000))) -- got 183.413000000000011, expected 183.413
Try this ...
atom a a = 183.4126 ? round(a,1) ? round(a,10) ? round(a,100) ? round(a,1000)
The issue you are seeing is that the "to_string" function outputs the number to the maximum number of decimals it can but the "?" statement only outputs a few decimal places.
The problem is that the rounded values cannot be exactly implemented in the IEEE floating point system that Euphoria uses. This can be demonstrated by this code ...
? atom_to_float64( round(a, 1000) ) ? atom_to_float64( 183.413 )
In both cases above, you should get {240,167,198,75,55,237,102,64} which is the IEEE encoding for the nearest number to 183.413.
The rule-of-thumb is only use floating point numbers if you are prepared to accept a margin-of-error in your calculations. If you are working with currency, this is obviously not acceptable, in which case you need to only work with currency values as 'cents' and format them for output using dollars AND cents.
7. Re: Bug in math.e?
- Posted by LarryMiller Nov 30, 2010
- 1300 views
The round() function controls the precision of a number, not how it will be displayed. If you wish to display a specific number of digits you should use a function like sprintf() or format(). These functions will give the results you expect.
8. Re: Bug in math.e?
- Posted by Anthill Nov 30, 2010
- 1260 views
sprintf should work just fine. I am still getting use to eu but am making a lot of progress.
Thanks for everyones input!
