Re: Re: Number of decimals

Apologies to group for one of those "scattered" replies.

On 18/09/10 00:02, Marianne wrote:
>
>
>
>
> Hi Daz and Mike
>
> Thanks for the response but BC will not help me. I apologise if my
> knowledge is not up to date or standard.
>
> I am using Gui4Cli currently for all calculations as I can perform all
> calculations in Gui4Cli.

Floating Point Arithmetic (FPA) is notoriously error-prone in many computer
implementations. Here's one explanation:
http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems


> Secondly I am a self studied programmer and do
> not know a lot about programming. I only know a little Basic. Here is an
> example and if I am off target please let me know.
>
> Take the following example:
> A = 1
> B = 1.538
>
> So A/B = 0.649772579597141...... and I want to round this off say to 8
> decimals. I cannot do the following:

That result is already inaccurate (before rounding) :(

Copy/Paste the following into the bottom box at:
http://sciencesoft.at/bc/?lang=en
--------------------------------------------
a = 1
b = 1.538
g4cans = 0.649772579597141
a/b
a/b - g4cans
--------------------------------------------
and click "Calculate"

Result:
.65019505851755526657 .00042247892041426657

That's a g4c inaccuracy of .00042247892041426657 on that one
calculation.

( I get the answer of around .65019506 in three other programs. )


>
> C = $($A/$B) = 0.649773 and send C to the external program, say BC,
> because Gui4Cli already rounded $C to 6 decimals. I can probably send
> $A/$B to BC (not tested yet as calculations are sometimes lenghty in
> statisics and not that easy to do it this way, if possible. (Will not be
> possible if one uses loops for example.)
>

I would recommend staying away from the in-built FPA and, instead,
call an external program (designed for the task) via [DOS.DLL] passing
FP-like numbers as strings.
Once your FP calculations are done and rounded, then you can
present the results in your gui as strings in the precision required.

> In other words it seems to me that all calculations therefore have to be
> performed with an external program if you want rounding off to more than
> 6 decimals. Although Gui stands for Graphical User Interface that is not
> what I want. (The majority of other languages do have a Gui interface,
> but I like Gui4Cli because of its simplicity.

FP = major complexity :) - no fault of Gui4Cli.
Use Gui4Cli with a reliably accurate external library routines for FPA.

>
> Why do I need so many decimals? This is to perform for example
> convergence problems of Functions, like probabilities and one will be
> suprised how quick Gui4Cli is.(My standards)
>
> If Gui4Cli can give decimals to more than 6 or if a new command such as
> 'Set Decimals to $value' can be added it will be great but I do not know
> how easy or difficult it will be.

It would be a daunting task, I think.
Take your example which I gave to BC:
What value would more decimal places on the end of an already
inaccurate result be? ;)

In other scripting language forums, I've seen strong
recommendations for avoiding doing currency calculations
in FPA (e.g. 7.55eur). Instead, they suggest do all calculations
in cents (755c) because you can't get unexpected rounding
anomalies using integer arithmetic (only programming bugs).

>
> Regards
>
> Frans
>

To you, also.

daz


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