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Yngvi
and everyone reading that (esp. Ken),
regarding (1)
me guessed that it would be too complicated to
allow the user to choose from the fp precision.
Instead it would be more suitable to have TWO
versions. The first is as is, the other, new one,
would be different in that it is using doubles.
May be it required only the replacement of
a few .dll files.
What me was using to do was having a type
template for EVERY floating type, i.e.,
e.g.,
typedef single THISFLOATTYPE
or
typedef double THISFLOATTYPE
This would just require one typist to replace
any existing floating point type definition
like 'single' or 'float' to e.g. THISFLOATTYPE.
Past the end of this typing (ouch...) it was
easy to compile 2 different retail versions.
It would then just be required to ship it to
a few friends only (first one of being
Guy Tann) ... Should been of possible, no?
(2) see above
Just my 2 cents - JR
----- Original Message -----
From: "Yngvi Hardarson" <hardy@xxxxxxxxxxxxx>
To: <metastock@xxxxxxxxxxxxx>
Sent: Donnerstag, 7. September 2000 21:29
Subject: RE: First calculation problem
> Ken!
>
> (1) Wouldn't it be possible to leave it to the user to decide whether he
> wants
> to use single or double precision floating point calculations, e.g. via a
> setting in the Tools/Options menu?
>
> This would enable those with the hardware resources and accuracy
> requirements
> to use double precisions and others to stick with single precision. I
recall
> from
> my days using statistical and econometric software on mainframes that some
> of those
> applications actually gave you the choice of precision. Then my computing
> bill would
> depend on my choice as well as the time it took to complete the
> calculations.
>
> (2) You have stated that some requests for features brought up by members
of
> the list
> are not commonly requested by the mass of users. In my opinion the mass
> opinion doesn't
> matter as much as input from "power users" of this list. The mass doesn't
> realize what
> a tremendous value there would be in implementing some of the suggestions
> put forth on
> this front. The mass might realize the value once you implement the
features
> and the
> mass might become even bigger.
>
> Best regards,
> Yngvi Hardarson
> hardy@xxxxxxxxxxxxx
>
> P.s. Many thanks to you for sticking to the list Ken. I believe you may
have
> greater
> influence on the application features than you say yourself, directly or
> indirectly.
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
> [mailto:owner-metastock@xxxxxxxxxxxxx]On Behalf Of PD Manager
> Sent: Thursday, September 07, 2000 15:18
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
>
> Guy:
>
> Through all the arguing both directions and all of the shots from people
on
> the sidelines it all boils down to the fact that we are using single
> precision floating point numbers and your other software is using double
> precision. Both methods have errors (as evidenced by your example and
> mine), but double precision does manage to provide more precision and
> therefore manages to hide the problem a little better.
>
> The differences you are seeing are based on the differences between single
> and double precision. As I have stated, we have considered going to
double
> precision but it comes at a cost in computer resources and therefore we do
> not take the decision lightly. Also, double precision does not guarantee
> absolute accuracy. If we went to double precision, we would only be
> duplicating the errors that appear in other double precision based
> applications. I would agree that the precision of MetaStock would indeed
> improve but if you are interested in ABSOLUTE accuracy of your
computations,
> you are going to have to avoid floating point calculations altogether,
> regardless of which software package you use. Unfortunately, to do that
you
> are going to have to use more traditional programming languages and write
> your own math routines that use scaled integers or BCD or something along
> those lines. You could do this with our MSX capability, but again, you
> would have to program at a lower level. Based on your credentials, I
don't
> think it would be a problem but only you could decide if it would be worth
> the effort.
>
> We all have to remember that engineers designed the floating point format
> (IEEE standard) and they can usually get away with "close enough". That
is
> unacceptable to the mathematicians however. The 8.999999999999999999
value
> is "close enough" to 9 for an engineer, but to a mathematician, it just
> doesn't work.
>
> I sympathize with your dilemma and I apologize if I have seemed too
> defensive about the issue. Believe me, I fight with the issue of
precision
> every day and I have thrown a few heated comments myself.
>
> We may indeed go to double precision numbers in the future but only if we
> can minimize the impact on the large percentage of our users who are
already
> "running on the edge" of their computer resource capacity. In the
meantime,
> I am finished with the jousting. If I can help you find the accuracy you
> want in MetaStock, I am more than willing to help. Feel free to email me
> privately and I will do all I can.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Guy Tann [mailto:grt@xxxxxxxxxxxx]
> Sent: Wednesday, September 06, 2000 5:38 PM
> To: metastock@xxxxxxxxxxxxx
> Subject: RE: First calculation problem
>
>
> Ken,
>
> Fine. I'll grant you your example. Now if you take the results of that
> cell and multiple it by some other cell, does Excel multiply by .9 or
> .899999999999? I'm interested in how Excel handles subsequent
calculations.
>
> In my tests, they appear to use the .9 as opposed to.8999999999 like MS,
> otherwise I wouldn't be able to create output that matches exactly the
> output from Clipper code and from TAS. All I know is that somewhere in
all
> three of these other languages, they have somehow managed to be able to
> "handle" any problems of this type. Right now I'm comparing my MS output
to
> output from Clipper (Spring97 version, I believe) running under DOS. I
had
> hoped that in working with a more "modern" language I could eventually
drop
> all of our DOS stuff.
>
> Ken, I guess what I'm saying is provide us with the same Floating Point
> Error Masking in Excel so that we can eliminate these problems. Let those
> who don't want it turn it off the same way Excel does.
>
> Guy
>
> " When I die, I want to go peacefully like my grandfather did, in his
sleep.
> Not yelling and screaming like the passengers in his car."
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of PD Manager
> Sent: Wednesday, September 06, 2000 8:02 AM
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
> Guy:
>
> What I have been saying all along is that numerically, in your computer
> (regardless of which software you are using) there are floating point
> rounding errors. Here is an example for Excel 2000:
>
> 1. Enter the following in a cell: =(43.1-43.2)+1
> 2. Using the Format Cells command TO TURN OFF THE FLOATING POINT ERROR
> MASKING THAT EXCEL DOES BY DEFAULT, change the format of the cell to show
> Scientific 15-digits precision. This accurately displays the format that
> the number is stored in in your computer. There is no masking of the
output
> (to hide the floating point error inherent in all floating point
> calculations) before display.
> 3. Look at the result. To you and I it is supposed to be 0.9. Excel,
> however, shows that the internal floating point representation is
> 0.899999999999999.
>
> The errors that you worry about are always there. Excel, by default, sets
a
> cell format that hides these errors from you. In MetaStock, we chose not
to
> try and determine the absolute precision that anyone wanted to see. We
> provided the Round() and Prec() functions to let the formula writer
> determine that for themselves.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Guy Tann [mailto:grt@xxxxxxxxxxxx]
> Sent: Tuesday, September 05, 2000 6:53 PM
> To: metastock@xxxxxxxxxxxxx
> Subject: RE: First calculation problem
>
>
> Ken,
>
> All I'm saying is my point has absolutely nothing to do with rounding.
This
> calculation works, without fail, in Excel. To make sure, I went back and
> did a couple of thousand of them and Excel never made an error. Now, I
> don't know how they were handling it internally, I only know how they
> presented and used the results correctly and that's all I care about.
> Regardless of all of the documentation you have presented, only MS has the
> particular problem I have presented.
>
> The other software never once failed to subtract properly. They never
once
> failed to provide me with a two decimal result even if I specified a 4
> decimal precision result field. And finally, they never once failed to
use
> the correct result with future calculations (which I think is the most
> important point and what you are missing).
>
> Again, I think you are confusing effort with results. Regardless of how
you
> represent the number internally, you are displaying it wrong and you are
> using the wrong value in further calculations. If any of these other
> languages or packages performed such simple arithmetic functions like
> subtraction similarly to MS, they have smarter internal algorithms to
insure
> that the results as presented are correct and are used correctly
internally.
> Something that MS is missing.
>
> The Microsoft article you referred me referenced rounding. My situation
has
> nothing to do with rounding, other than with what you refer to as the
> implied internal processing. There is no rounding necessary when
> subtracting a 2 decimal number from another 2 decimal number. Now you can
> cop out saying that internally, single precision may or may not represent
> the values correctly. That's irrelevant. If I bought a $2.99 calculator
> and ran this calculation, the entire batch of calculators would be
scrapped
> as defective. I consider MS to be defective, just like those calculators,
> until this problem is fixed!
>
> Now, if I was doing more sophisticated calculations I have no problem
> handling my own rounding and controlling my own precision. I do this all
> the time in other languages. My Clipper code, for example, has all of
that
> coded and it works without a problem. I've been doing this on
> microcomputers for over 25 years. In Clipper, for example, I haven't had
to
> add tons of code to insure that their basic functions (+ and -) calculate
> correctly. My complaint with MS is that I shouldn't have to build in all
> sorts of controls to compensate for MS' inability to perform basic
> arithmetic. Once I get past simple arithmetic, I have no problem handling
> rounding and precision. What I can't tolerate are errors in basic
> representation of my beginning calculations. If you'll notice, I
> specifically used the same input in testing Clipper, MS and Excel. I also
> used the same computer, CPU, memory and disk drive in order to eliminate
any
> external influencing factors. By carefully controlling my environment,
I'm
> able to drill down to the exact point where MS failed. And surprise, it
was
> a simple subtraction. No ifs ands or buts, the answer is wrong. Again,
you
> can try to hide behind single precision, or whatever representation you'd
> like, but a wrong answer is a wrong answer. If all of these other
languages
> have this same problem, why does it only appear in MS? It seems to me
that
> they are doing something right and that you guys are missing something.
> Continuing this discussion is a moot point. We should be looking at what
we
> (either us users or you at Equis) need to do in order to put the code into
> the system to fix this problem, and believe me it is a problem, especially
> if you are trading over 6 figures.
>
> Maybe it's me, but does anybody here not think this is a problem? If I'm
> the only one who thinks that MS should be able to subtract two numbers and
> come up with a correct answer is important, then I apologize and will pack
> up my stuff and leave. If the people developing systems think that 4 - 2
=
> 1.9999999 is OK and that they're able to use that number in further
> calculations without a problem, then either they aren't working with the
> precision required by our system, or they have somehow been able to
develop
> a methodology to filter these errors out as noise. Regardless, we require
> slightly more accuracy.
>
> If your answer is, we get as close as we can and are limited by the
> limitations of single precision and don't really care that everyone else
> does it correctly, we're happy being close, then just say that and I won't
> waste any more time. If on the other hand, you understand that your
> response is not sufficient and you are going to take some action to fix
> this, say that. I think we have beaten this into the ground enough and
> unless you agree that there is a problem, I'm going to move on. No sense
> beating my head against a wall, especially if Equis' Programming Manager
> doesn't think there is a problem. I'll know that MS is strictly a
charting
> program and that it can't be used for developing serious trading systems,
> since it can randomly impact your testing by generating noise.
>
> No problem, I'll just write off all of the time I've spent trying to get
our
> stuff running in MS and move on to one of the other languages I own.
>
> Guy
>
> " When I die, I want to go peacefully like my grandfather did, in his
sleep.
> Not yelling and screaming like the passengers in his car."
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of PD Manager
> Sent: Tuesday, September 05, 2000 3:36 PM
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
> Guy:
>
> This is a direct cut and paste from a Microsoft Product Support Services
web
> site. All I am saying is that I understand your frustration from
precision
> errors. I am also saying that virtually all software suffers from the
same
> problem. I provide this in hopes that everyone will realize that floating
> point errors are not unique to MetaStock.
>
> http://support.microsoft.com/support/kb/articles/Q196/6/52.asp
>
> ----------------------------------------------------------------------
>
> Floating Point Limitations
> All of the rounding implementations presented here use the double data
type,
> which can represent approximately 15 decimal digits.
>
> Since not all fractional values can be expressed exactly, you might get
> unexpected results because the display value does not match the stored
> value.
>
> For example, the number 2.25 might be stored internally as 2.2499999...,
> which would round down with arithmetic rounding, instead of up as you
might
> expect. Also, the more calculations a number is put through, the greater
> possibility that the stored binary value will deviate from the ideal
decimal
> value.
>
> -----------------------------------------------------------------------
>
> Also below is another cut and paste from Microsoft
> http://support.microsoft.com/support/kb/articles/Q125/0/56.ASP
>
> There are many situations in which precision, rounding, and accuracy in
> floating-point calculations can work to generate results that are
surprising
> to the programmer. There are four general rules that should be followed:
>
> In a calculation involving both single and double precision, the result
will
> not usually be any more accurate than single precision. If double
precision
> is required, be certain all terms in the calculation, including constants,
> are specified in double precision.
>
>
> Never assume that a simple numeric value is accurately represented in the
> computer. Most floating-point values can't be precisely represented as a
> finite binary value. For example .1 is .0001100110011... in binary (it
> repeats forever), so it can't be represented with complete accuracy on a
> computer using binary arithmetic, which includes all PCs.
>
>
> Never assume that the result is accurate to the last decimal place. There
> are always small differences between the "true" answer and what can be
> calculated with the finite precision of any floating point processing
unit.
>
>
> Never compare two floating-point values to see if they are equal or not-
> equal. This is a corollary to rule 3. There are almost always going to be
> small differences between numbers that "should" be equal. Instead, always
> check to see if the numbers are nearly equal. In other words, check to see
> if the difference between them is very small or insignificant.
>
> ------------------------------------------------------------------------
>
> What I have said all along is that we chose not to mask the errors (by
> assuming how much precision our customers want) because our users have
such
> a wide range of precision that they require. We provided the tools for
our
> users to determine their own precision in calculations. You can get
> COMPLETELY accurate results from MetaStock but you have to do some extra
> programming in the formula language to get it. We chose simply to make no
> assumptions about how much precision our formula writing users would
> require. We gave them the tools to apply precision for themselves.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Guy Tann [mailto:grt@xxxxxxxxxxxx]
> Sent: Tuesday, September 05, 2000 12:22 PM
> To: metastock@xxxxxxxxxxxxx
> Subject: RE: First calculation problem
>
>
> Ken,
>
> I understand what you're saying completely. You have missing my point
> entirely.
>
> As a user, I really don't care how the numbers are represented internally.
> I just care that the answers are CORRECT. Again, in order to reemphasize,
> you have missed my point entirely. The other software I have, including
> several different programming languages, all manage to provide the correct
> results, regardless of how they're represented internally. If, as you
say,
> the other software only modified the results before displaying them or
> played some other internal game and still maintained the single precision
> result internally, then all of their subsequent calculations would be off
by
> the same amount as MS (0.2) for each calculation, since they would be
using
> this internal, erroneous result. My point that you're missing, is that
> these other languages, regardless of precision, are able to not only
display
> the correct result (and I really don't care how they do it), they are also
> able to use that correct result internally in subsequent calculations,
which
> MS DOESN'T!
>
> So, I guess I still don't understand your point. Having majors in
> Mathematics, Statistics, and Economics, and having almost 40 years
> experience programming (my first job was as a Systems Engineer at IBM),
this
> is very frustrating. While I admit to getting older, I still haven't
> reached my dad's 91 years yet. My 10 year old, my brother and I, and my
> "old man" (who refuses to use MS because of this) still can't understand
how
> every other package or language we have is able to subtract two numbers
and
> use the results in further calculations without a problem regardless of
what
> is taking place internally. Notice I'm not referring to just what is
> displayed.
>
> If we were talking theory or some esoteric mathematical methodology, I
> understand that 2.379999999 can accurately approximate 2.38, a real world
> number. In calculus and statistics, I'm used to getting close but not
exact
> results as n goes from 1 and approaches infinity. We're talking
subtraction
> and 2.379999999 is NOT the correct result of the calculation 14.89 - 12.51
=
> 2.38, regardless of whatever planet you're on. More importantly, any
> further calculations that use the result of that first subtraction should
> use 2.38 and not 2.379999999! Again, all of my other software has managed
> to figure out that they not only need to display the correct answer but
that
> they also have to use that correct answer in further calculations.
>
> What about this is so hard to understand?
>
> Regardless of precision, any language that purports to provide basic
> arithmetic capabilities should be required to provide correct results.
> Again, this internal representation of numbers is not the issue here; it's
> what you display and what you use internally in subsequent calculations.
>
> The bottom line is, MS contains a major flaw insofar as it is unable to
> perform simple arithmetic and use the results in subsequent calculations.
> You should put a warning on MS stating this, much like the warning on
> cigarettes. Something like, even though MS uses single precision
arithmetic
> like Excel and others, it is unable to duplicate their results, which may
> affect your financial health. Seriously, can you see what I'm saying?
What
> you display and how you display it is symptomatic of a more invasive
> problem. What you display is also what you use in your further
> calculations, and since you have calculated an incorrect result, all of
your
> subsequent calculations will be wrong. This is the problem, and in my
mind,
> a very significant one.
>
> Guy
>
> " When I die, I want to go peacefully like my grandfather did, in his
sleep.
> Not yelling and screaming like the passengers in his car."
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of PD Manager
> Sent: Tuesday, September 05, 2000 7:41 AM
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
> Guy:
>
> Regardless of where the numbers come from (download, keyboard or wherever)
> the error occurs when the numbers are translated from the ASCII
> representation and stored in the machine. The other software packages
> suffer from the same problem. What they have chosen to do is to
> automatically mask the problem by truncating the OUTPUT before display. I
> assure you that INTERNALLY, the numbers are the same. MetaStock does not
> modify the output numbers. Regardless of the software package, the
internal
> storage is a HARDWARE approximation of a floating point number. Some
> software packages simply truncate and round the output BEFORE DISPLAY to
> mask the problem away from the user. The approximation and the associated
> accuracy problems are still there.
>
> Some software packages will use double precision floating point numbers to
> help improve the accuracy of floating point representation. As I said,
this
> comes at the cost of double the memory requirements.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Guy Tann [mailto:grt@xxxxxxxxxxxx]
> Sent: Monday, September 04, 2000 6:28 PM
> To: metastock@xxxxxxxxxxxxx
> Subject: RE: First calculation problem
>
>
> Ken,
>
> Sorry for the delay, but my DSL modem crapped out and then I was visiting
> Murder City until today.
>
> I wasn't typing anything into the computer. I used Equis' Downloader and
> Reuter's data service to download my data. I then use MS to massage it.
> Interestingly, TAS uses the Downloader data as well without any of these
> problems. Using OLE to access the data in Excel works properly as well.
It
> appears that these other software packages manage to keep track of the
> correct number of decimal places, whereas MS just sort of goes with the
flow
> and takes whatever it might find stored. I really don't care as long as I
> know that accuracy isn't one of MS' strong suits. I can understand your
> points, but in working with many programming languages, they all manage to
> do something to keep track of significant digits without barfing. Again,
if
> I was doing anything complex, I could understand your point completely,
but
> the inability to subtract two numbers and consistently come up with the
> correct answer is still hard for me to fathom.
>
> Anyway, here is a sample of some of the code I've had to use to get around
> this in one instance. By the way, none of my other programming languages
or
> Excel require these mechanizations. It appears that MS was designed as a
> charting or graphics program with computational capabilities added as an
> afterthought. What we need to remember is that if we want to use it as
> such, we'll need to work around its deficiencies ourselves.
>
> COMN0:= C - COMMODLOW; {simple subtraction of C - L}
> COMN:= PREC( If( COMN0 > 0 , (COMN0+.005), If( COMN0 < 0 , (COMN0 - .005 )
,
> COMN0 )) , 2 ); {needed to fix MS inability to maintain significant
digits}
> COMN1:= COMN / COMAR; {simple divide}
> COMN2:= COMN1 - .5; {Simple subtraction}
> COMN3:= COMN2 * 2; {simple multiplication}
> COMN3R:= If( COMN3 > 0 , (COMN3 + .00005 ) ,
> If( COMN3 < 0 , (COMN3 - .00005 ) ,
> 0 ) ); {rounding to 4 decimal places performed manually}
> COMN4:= ( PREC( COMN3R, 4 ) * 10); {take answer to 4 decimals and
multiply
> by 10}
> COMN5:= If( COMN4 > 0 , ( COMN4 ) + .5 , If( COMN4 < 0 , ( COMN4 ) - .5 ,
> ( COMN4 ) )); {round to nearest whole number}
> COMY:= Int( COMN5 ); {store integer}
>
> This does work, albeit in a slightly confused manner and requires 8 more
> variables than it should. Using this fixed the one erroneous calculation
I
> had and let me move on for further testing.
>
> OTOH, I am now working on trying to get the Ref() function to work per the
> manual and will try to get some time to spend on it tonight if I can stay
> awake. I was up at 4AM Detroit time (1AM local time) and have over 400
> e-mails to wade through since 8/29 (most of which I deleted).
>
> Guy
>
> " When I die, I want to go peacefully like my grandfather did, in his
sleep.
> Not yelling and screaming like the passengers in his car."
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of PD Manager
> Sent: Tuesday, August 29, 2000 10:05 AM
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
> Guy:
>
> The precision error occurs as soon as the number is stored in your
computer.
> If you are typing a number into a computer (such as 12.1), as soon as that
> number is stored in a single precision floating point number in your
> computer, the precision error is there. The number is already stored as
an
> approximation. This is a CPU / hardware issue and is not related to the
> software itself.
>
> Most software will mask this error by doing rounding of a floating point
> number before it is displayed. In the case of the 1469.3999999, if you
ask
> a computer to display that number with two digits to the right of the
> decimal point, rounding occurs and you will see 1469.40, but the number is
> actually stored in the computer as 1469.3999999. This is true even if you
> entered a number at the keyboard (or downloaded the number or read it from
> some other source) that was 1469.40.
>
> The difference between MetaStock and your other packages is that the other
> software is performing the rounding before the results are displayed on
the
> screen. MetaStock is not doing this and is displaying the numbers out to
> the maximum possible length. I assure you that if other software packages
> are displaying 1469.40, the internal representation is actually
> 1469.3999999. The approximation and actual storage of the numbers is a
> function of the CPU hardware and not the software package itself.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Guy Tann [mailto:grt@xxxxxxxxxxxx]
> Sent: Monday, August 28, 2000 12:34 PM
> To: metastock@xxxxxxxxxxxxx
> Subject: RE: First calculation problem
>
>
> Ken,
>
> I guess I still don't understand what's happening here.
>
> These numbers were downloaded from Reuters and were stored in the O, H, L,
C
> data arrays, all handled internally by Equis. My assumption is that these
> numbers were downloaded properly and that they contain only the two
decimal
> places shown in the data and in the data window. Going out and looking at
> the numbers in Downloader and in the related Chart supports that
assumption.
> Is that an invalid assumption? These numbers only have two decimal places
> to begin with. Did MS somehow managed to "modify" the original input and
> store them as something like 1469.3999999?
>
> If that's the case, then using Precision in order to insure that simple
> arithmetic calculations to maintain the two decimals places appears to be
a
> requirement.
>
> Generally, there are very few problems occurring, but they are sufficient
to
> throw off some of our results.
>
> We have these calculations running in Clipper, Excel, COBOL, and TAS
without
> problems.
>
> We only have three different levels of precision in our system and they
are
> 0, 2, and 4. We either use the Rnd() function or in cases like the one
I'm
> working on right now, manually code our own rounding.
>
> Guy
>
> " When I die, I want to go peacefully like my grandfather did, in his
sleep.
> Not yelling and screaming like the passengers in his car."
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of PD Manager
> Sent: Monday, August 28, 2000 8:15 AM
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
> Isn't programming with floating point numbers fun? <g>
>
> Floating point errors tend to compound as more calculations are performed.
> I could write an entire book on the subject (I'm sure there are books
> written on just this subject). Typically, floating point numbers are
> guaranteed to have 6-7 digits of precision. When you start doing
> mathematical operations on these numbers, there are times when some of
these
> strange issues will creep in.
>
> What I have found is that you should use the precision function only if
you
> are trying to compare floating point numbers. Otherwise just stick with
the
> standard calculations.
>
> What is amazing is that although your numbers look good to start with
> (1486.20 and 1469.40) the error is probably already there. The actual
> numbers stored in the computer may already be something like
(1486.20000001
> or 1469.3999999). Usually when these numbers are prepared for output
> (display or printed) the software will perform rounding to get them to
look
> like the numbers you entered. When you perform a mathematical operation
on
> these numbers, the error becomes more apparent so that the rounding before
> output didn't make your result look correct.
>
> Virtually any computer that stored floating point numbers has this
problem.
> I worked on flight simulations for several years and the only way we could
> get around the problem was to do EVERYTHING in integer math and keep track
> of assumed decimal points.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Guy Tann [mailto:grt@xxxxxxxxxxxx]
> Sent: Sunday, August 27, 2000 1:50 AM
> To: metastock@xxxxxxxxxxxxx
> Subject: RE: First calculation problem
>
>
> Ken,
>
> Are you saying that I need to add the prec() function to each one of my
> variable calculations? Does this problem compound when building systems
> using calculations upon calculations or will the prec() function used at
> each level take care of the problem?
>
> Guy
>
> Never be afraid to try something new. Remember, amateurs built the ark,
> professionals built the Titanic.
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of PD Manager
> Sent: Friday, August 25, 2000 7:35 AM
> To: 'metastock@xxxxxxxxxxxxx'
> Subject: RE: First calculation problem
>
> MetaStock does indeed use single precision floating point numbers. As you
> mentioned, going to double precision would literally double the memory
> requirements for data storage for charts and would also slow down
> calculations. When you get into mathematical calculations, however, going
> to double precision doesn't necessarily make the problem better. PC
> computer hardware still cannot accurately store a number as simple as 0.1
> whether you are using single or double precision. It is stored as an
> approximation. When it comes to floating point numbers, the hardware can
> really only accurately store fractional numbers that are powers of two
(1/2,
> 1/4, 1/8, 1/16 etc).
>
> Other software packages suffer from the same problem (including VB and
> Excel) although some manage to mask it better than others. If you don't
> believe this, I can submit a set of "simple" calculations that will cause
> Excel to show precision errors also.
>
> Some software packages will use other methods to store and/or calculate
> floating point numbers. This usually involves something like BCD encoding
> or some type of integer encoded fixed point real numbers. While this
> ultimately solves the precision problem, it has other problems with speed
of
> calculations as well as a reduced ability to store large or very small
> numbers.
>
> We have always been aware of this issue and that is why we added the
> precision function to the formula language. It was put there in an
attempt
> to help those writing formulas to work with the precision they needed.
>
> Ken Hunt
> Programming Manager
> Equis International
>
>
> -----Original Message-----
> From: Kent Rollins [mailto:kentr@xxxxxxxxxxxxxx]
> Sent: Friday, August 25, 2000 12:40 AM
> To: metastock@xxxxxxxxxxxxx
> Subject: Re: First calculation problem
>
>
> Looks like you may have hit the old single-precision problem. PCs
basically
> have 3 native ways of storing floating point numbers: single-precision (4
> bytes), double-precision (8 bytes), and long double (10 bytes). The
problem
> is that each one of these representations has a limited number of
"numbers"
> that it can represent and from time to time you will hit a calculation
that
> reveals this limitation in all it's splendor. Single-precision floats can
> represent approximately 4 billion different numbers. That's a lot until
you
> consider that between 0 and 1 there are an infinite number of floating
point
> numbers. Double-precision has many, many more number that it can
represent
> (4 billion times 4 billion) and you RARELY see the kind of error you have
> hit when you are dealing with numbers on the scale of 1486 with only 2
> places of precision. That leads me to suspect that Equis is using
> single-precision numbers for these calculations (Omega does the same
thing).
> Saves memory, SLIGHTLY faster in computation, loses precision. There is
> really no good reason for using singles in an app like this and there is a
> (now obvious) good reason not to. I would scream and yell at Equis. Tell
> Little Guy that if he convinces Equis to use doubles you'll buy him a pony
> and then drop him off in the programmer's offices.
>
> Ken Hunt, does MetaStock use single precision for these calculations?
>
> Kent
>
>
> -----Original Message-----
> From: Guy Tann <grt@xxxxxxxxxxxx>
> To: Metastock User Group <metastock-list@xxxxxxxxxxxxx>
> Date: Friday, August 25, 2000 1:29 AM
> Subject: First calculation problem
>
>
> List,
>
> Well, I decided to do a little more work and discovered my first problem.
>
> Somehow, MS came up with the following:
>
> 1486.20
> - 1469.40
> 16.7999 instead of the more commonly expected 16.80
>
> Now the first number is the Close and the second number is the day's low,
so
> we can't blame this on any previous calculation or anything left over from
> something else. Well, that's not quite true. The Low used in the
> calculation was the result of an IF() statement that made sure that the
Low
> was really the Low by our definition (by checking it against the previous
> day's Close).
>
> What internal methodology might cause this excellent bit of subtraction?
>
> Granted, in checking out the 170-member dataset, I didn't check them all.
I
> checked the first 20 and the last 20. Now I'll probably have to go back
and
> sample some in the middle.
>
> I used my trusty, solar powered calculator to double-check my Clipper
output
> and they both agree that MS is wrong. Any suggestions?
>
> This is making me very nervous and might force me back to Excel and/or VB.
> So far I've spent over two week on this relatively simple program and I
have
> to admit that I never thought it would be necessary to go back and
> double-check such basic arithmetic.
>
>
> Guy
>
> Never be afraid to try something new. Remember, amateurs built the ark,
> professionals built the Titanic.
>
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