-0.00 Sum

[chrislegarth]

I have an odd thing I have encountered when adding a list of numbers with the resulting sum being -0.00.
I'm able to get the same -0.00 when adding negative numbers or subtracting positive numbers.

When I subtract 31.24 partway through the list the result is 0.00 as I expected.

Thoughts on the -0.00?  Is this expected?

Code (winbatch) Select Expand


decimals(2)
amount = 0
amount = amount + 12.01
amount = amount + 12.90
;amount = amount + -24.91
amount = amount - 24.91
amount = amount + 13.15
amount = amount + 14.60
amount = amount + 3.67
;amount = amount + -31.42
amount = amount - 31.42
amount = amount + 2.28
amount = amount + 2.24
;amount = amount + -4.00
amount = amount - 4.00
amount = amount + 2.61
amount = amount + 2.26
amount = amount + 1.25
amount = amount + 1.23
amount = amount + 1.28
amount = amount + 1.25
;amount = amount + -10.40
amount = amount - 10.40
message("",amount)


[td]

Is there an issue here? After all -0.0 == 0.0.

{edit} Should have mentioned that you will get a different result when you remove the "decimal(2)" line. The full floating point result is a very small negative number.

[chrislegarth]

It is just a display issue as the numbers represent currency and no one expects to see -0.00.
I guess I'm just wondering why the last operation results in a tiny negative number when the others do not.

Sum Output
12.01
24.91
0.0
13.15
27.75
31.42
0.0
2.28
4.52
0.52
3.13
5.39
6.64
7.87
9.15
10.4
-1.77635684e-015

[td]

You would need to have a basic understanding of how floating point numbers are represented on binary systems to effectively answer that question. Basically, real numbers have values that fall between two digits in binary systems. It would take an infinite number of bits to accurately represent all real number between two integers. This leads to representational errors that are not just an issue for WinBatch. This is an issue common to all computers using  IEEE 754 standard based floating point number machine instructions.

In the standard "Zero is a special value denoted with an exponent and mantissa of 0. -0 and +0 are distinct values, though they both are equal."

[td]

A quote from this paper https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html that explains it much better than I can:

"Squeezing infinitely many real numbers into a finite number of bits requires an approximate representation. Although there are infinitely many integers, in most programs the result of integer computations can be stored in 32 bits. In contrast, given any fixed number of bits, most calculations with real numbers will produce quantities that cannot be exactly represented using that many bits. Therefore the result of a floating-point calculation must often be rounded in order to fit back into its finite representation. This rounding error is the characteristic feature of floating-point computation."

[kdmoyers]

This is fun: go to https://www.h-schmidt.net/FloatConverter/IEEE754.html
and type in some of your values.  I was amazed.  No wonder banks and such
try not to store money values in floating point numbers.

[ChuckC]

Why am I reminded of this?

https://filmschoolrejects.com/getting-rich-with-richard-pryors-banking-scheme-from-superman-iii-7811840a8a0/

[td]

It is just a display issue as the numbers represent currency and no one expects to see -0.00.
I guess I'm just wondering why the last operation results in a tiny negative number when the others do not.

Sum Output
12.01
24.91
0.0
13.15
27.75
31.42
0.0
2.28
4.52
0.52
3.13
5.39
6.64
7.87
9.15
10.4
-1.77635684e-015

Should have mentioned that to remove the "-" sign from a the 0.00 result is to do something like this

Code (winbatch) Select Expand

if amount == "-0.0"
   amount = StrClean(amount, "-", "", 0, 1)
endif

Using a string for the minus zero value for the right-hand side causes the amount value to be rounded before the comparison is made. Of course, the rounding is the result of the Decimals function.

[chrislegarth]

Thanks Everyone!

Tony- I did something similar to handle it that seems to work as well.

Code (winbatch) Select Expand

if amount == -0.00 then amount = 0.00

[stanl]

Why am I reminded of this?

https://filmschoolrejects.com/getting-rich-with-richard-pryors-banking-scheme-from-superman-iii-7811840a8a0/

Good movie. Actually worked with a Commission program where certain calculations would be a penny off due to rounding error. I guess a more general question would be: if values were placed in Currency Type Object would the results still be the same as the floating point numbers the OP presented that created the issue?

[td]

Thanks Everyone!

Tony- I did something similar to handle it that seems to work as well.

Code (winbatch) Select Expand

if amount == -0.00 then amount = 0.00

Just remember that the Decimal function does not change the actual value of the amount variable in your example. It only changes the displayed value when the variable is converted to text.