Re: Number of decimals

Fred and Daz

Once again thanks for all the information.

This might sound strange but I am not that concerned about precision. I am more interested about the number of decimals shown.

I wrote a program in Gui4Cli to calculate the probabilities for the F-probability distribution, say for an F-value of 1.49 with Df1 = 3 and Df2 = 19. The answer should be 0.25

At one stage I perform a calculation with a variable with 7 decimals, something like 0.0000005.... This value is given as 0.000001 by G4Cli (rounded to 6 decimals. My final answer is 0.15??? using Gc4 instead of 0.24????

What I did then was to define the variable say A directly in Gui4cli  as A = 0.0000005 and repeat the calculation and I got the correct answer.(I just want to point out that I know that is not a problem of Gui4Cli.)

Fred, last night I wrote a dll using FreeBasic, testing it and it works fine. Unfortunately it is a system dll and not a "Gui4Cli" dll so one has to use the sysdll command. (I do not have a clue how to write a Gui4Cli dll, although I had a look at the dll tutorial.)

This dll will be app. 20 KB and includes the Normal, T-, F- Chi-Square, Gamma and other distributions also with the inverse functions, but I still prefer not to use dlls unless it is not possible to perform all calculations within Gui4Cli (I repeat, I like Gui4Cli.)

The majority of the above distributions work in Gui4Cli, except for the rounding in a few cases. 

Once again I want to thank all of you for the replies.

Regards.

Frans


--- In [email protected], "fredfjord@..." <fredfjord@...> wrote:
>
> Hi,
> 
> The expression evaluation uses 'sprintf (out, "%f", res))' at the end and the default precision is 6 digits for %f.
> I think the best solution would be to add a SET FLOAT witdh.precision statement by Dimitris with default .6 to keep compability.
> 
> Another solution would be to make a math dll, i can try to use the same module G4C uses for math in a dll with a greather precision.
> It can take a while since i have a cold and yesterday had 39,3 degrees so i don't think very fast :)
> I already did make the eval module as a command line tool so it should not be to difficult.
> 
> Using bc you would have a high precision calculator as long as you use only strings and no calculation in G4C.
> 
> Regards,
> Fred.
> 
> 
> 
> --- In [email protected], dazroo <daz4roo@> wrote:
> >
> > 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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