Re: This calculation is just wrong / computer can't count!

GT schrieb:


One more try.

We do not understand the rationale behind your desire to compare the
computer arithmetics to "real math" or decimal arithmetics.

Usually, when I need to do calculations in a computer program, I look at
the property (range, precision, resolution, accuracy) of source data and
the result I need. Usually I find that the more than 14 significant
digits of the double data type is more than I would ever need. So I do
my calculations. I then take the final result and format it myself to
the number of decimal digits I need to present to the user.
If I stick to the rules of basic floating point math on computers (some
of which have already been explained in this long thread) I can be quite
sure that the result I get is the result I expect up to the digit I
chose to present to my user. I would never care if the texual
representation of some interim results was wrong at the 14th digit if I
only need 6 digits in the result.

So we just don't understand why you actually insist of beeing exact in
decimal arithmetic. Any arithmetic is good if performed correctly, and I
would not care if the computer would use digits with a value of 3, 5 or
17 as long as the end result has more correct significant digits than I
need. So while a decimal number can not exactly be represented in
computer logic, it usually can be represented *exact enough* for most
applications.

So the question should be: Does the final result I get from my
calculation differ from the mathematically correct result with an error
of more than x% or not. If not, you should not care abotu errors in the
17th digit because they have no meaning for the end result.

If you think it has a meaning for the end result, maybe you can explain
again *why*, because I think this information has been lost in this long
thread.