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Jan 31, 2010, 4:54:54 PM1/31/10

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I defined a function for calculating probabilities of Poisson

distribution. When I try to calculate probability for large numbers

using floating point format I get incorrect results. The file with

screenshots is here: http://pics.livejournal.com/iosaaris/pic/0004w4hk.jpg

distribution. When I try to calculate probability for large numbers

using floating point format I get incorrect results. The file with

screenshots is here: http://pics.livejournal.com/iosaaris/pic/0004w4hk.jpg

The upper left screen shows how the function Poi() was defined. One

below shows the calculation of Poi(300, 200). At first it is

calculated symbolically and then the result is converted to floating

point number. In this case the result is correct. My TI-89 gives the

same result (two screenshots at right).

When I try to calculate the same function using floating point numbers

as input (lower left screen) I get significantly different result.

What is the problem or what am I doing incorrectly?

And one more question. When working in ALG mode with symbolic

expressions, is it there any way to get them simplified upon every

press of ENTER like TI-89 does? For example I enter:

X+5

then

ANS(1)^2-1

and I get

(X+5)^2-1

If I want to simplify it, I have to select it with arrows and press

ENTER again. How can I get it simplified when I enter ANS(1)^2-1

without pressing ENTER once more?

Jan 31, 2010, 7:11:52 PM1/31/10

to

In article

<b5482632-b245-4279...@m16g2000yqc.googlegroups.com>,

Dima <iosa...@gmail.com> wrote:

<b5482632-b245-4279...@m16g2000yqc.googlegroups.com>,

Dima <iosa...@gmail.com> wrote:

In the RPN mode, all you have to do is press the EVAL key.

You might try that in ALG mode and see what happens.

Feb 1, 2010, 10:56:01 AM2/1/10

to

On Jan 31, 4:54 pm, Dima <iosaa...@gmail.com> wrote:

> I defined a function for calculating probabilities of Poisson

> distribution. When I try to calculate probability for large numbers

> using floating point format I get incorrect results. The file with

> screenshots is here:http://pics.livejournal.com/iosaaris/pic/0004w4hk.jpg

>

> The upper left screen shows how the function Poi() was defined. One

> below shows the calculation of Poi(300, 200). At first it is

> calculated symbolically and then the result is converted to floating

> point number. In this case the result is correct. My TI-89 gives the

> same result (two screenshots at right).

>

> When I try to calculate the same function using floating point numbers

> as input (lower left screen) I get significantly different result.

>

> What is the problem or what am I doing incorrectly?

> I defined a function for calculating probabilities of Poisson

> distribution. When I try to calculate probability for large numbers

> using floating point format I get incorrect results. The file with

> screenshots is here:http://pics.livejournal.com/iosaaris/pic/0004w4hk.jpg

>

> The upper left screen shows how the function Poi() was defined. One

> below shows the calculation of Poi(300, 200). At first it is

> calculated symbolically and then the result is converted to floating

> point number. In this case the result is correct. My TI-89 gives the

> same result (two screenshots at right).

>

> When I try to calculate the same function using floating point numbers

> as input (lower left screen) I get significantly different result.

>

> What is the problem or what am I doing incorrectly?

Floating point numbers on the HP can't go higher than 10^499. In

addition, they are limited to 12 significant digits. You're computing

Poi(y,k) = e^(-y)*y^k/k!. So Poi(300,200) = e^-300 * 300^200/200!.

300^200 and 200! are far beyond the limits floating point numbers.

This is a very old problem with computers. The trick is to change the

order of evaluation. Instead of evaluating 300^200 and dividing by

200!, you need to evaluate (300/200)*(300/199)*(300/198)*...(300/2)*

(300/1). Sorry, I don't have the time right now to figure out exactly

how to do this.

It's too bad that HP doesn't supply a LNFACT() function where LNFACT

(x) = ln(x!). This is pretty easy to compute from ln(gamma(x)) which

can be computed directly. If you had LNFACT() then ln(POI(y,k)) = -y

+k*ln(y)-LNFACT(k), which are all reasonably sized numbers that can be

represented in the calculator. So POI(y,k) = e^(-y+k*ln(y)-LNFACT(k))

Dave

Feb 1, 2010, 4:10:10 PM2/1/10

to

I have been saying for YEARS that the HP calculators need a lngamma

function.

An easy way to do it yourself in user RPL would be to use ln(gamma(x))

for 0 < x < 100 or so,

and use Stirlings apporximation for larger x.

You can use Lanczos' approximation for all complex values with

positive imaginary part,

but it is more complicated.

Martin Cohen

Feb 3, 2010, 3:17:08 PM2/3/10

to

Visit http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv018.cgi?read=132639,

then scroll down to message #6. I posted a LogGamma and LambertW for

the 50g. They are written in C with a library front end. The memory

used in the 50g is on the order of bytes. The C programs will need to

be installed on the SD card. Complex values supported.

Feb 4, 2010, 4:42:09 AM2/4/10

to

Il 03/02/2010 21.17, data...@gmail.com ha scritto:

>

> Visit http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv018.cgi?read=132639,

> then scroll down to message #6. I posted a LogGamma and LambertW for

> the 50g. They are written in C with a library front end. The memory

> used in the 50g is on the order of bytes. The C programs will need to

> be installed on the SD card. Complex values supported.

>

> Visit http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv018.cgi?read=132639,

> then scroll down to message #6. I posted a LogGamma and LambertW for

> the 50g. They are written in C with a library front end. The memory

> used in the 50g is on the order of bytes. The C programs will need to

> be installed on the SD card. Complex values supported.

There is no special.zip in http://sense.net/~egan/hpgcc/misc/ !

Feb 4, 2010, 11:58:28 AM2/4/10

to

On Feb 4, 2:42 am, Simone.Cer...@gmail.com wrote:

> Il 03/02/2010 21.17, dataj...@gmail.com ha scritto:

>

>

>

> > Visithttp://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv018.cgi?read=13...,

> > then scroll down to message #6. I posted a LogGamma and LambertW for

> > the 50g. They are written in C with a library front end. The memory

> > used in the 50g is on the order of bytes. The C programs will need to

> > be installed on the SD card. Complex values supported.

>

> There is no special.zip inhttp://sense.net/~egan/hpgcc/misc/!

> Il 03/02/2010 21.17, dataj...@gmail.com ha scritto:

>

>

>

> > Visithttp://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv018.cgi?read=13...,

> > then scroll down to message #6. I posted a LogGamma and LambertW for

> > the 50g. They are written in C with a library front end. The memory

> > used in the 50g is on the order of bytes. The C programs will need to

> > be installed on the SD card. Complex values supported.

>

> There is no special.zip inhttp://sense.net/~egan/hpgcc/misc/!

Yikes! Thanks. Fixed now. I broke the link with some house cleaning.

Feb 4, 2010, 12:28:27 PM2/4/10

to

On 4 Feb, 17:58, "dataj...@gmail.com" <dataj...@gmail.com> wrote:

> Yikes! Thanks. Fixed now. I broke the link with some house cleaning.

> Yikes! Thanks. Fixed now. I broke the link with some house cleaning.

Thank you for HPGCC tutorial LambertW and LogGamma :-) .

Best regards,

Simone.

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