# Re: [Jprogramming] Integer-floating type change for large numbers in j805 and j806

I think that Don Guinn was referring to the fact that the output results from input of n sig figs will not be good to anything better than n sig figs. You have pointed out limits in the representation of base 10 integers in a base 2 system. In fact, the results of multiplying 2 4 digit numbers might result in an overflow or conversion to float with truncation.
```
Don Kelly
On 2017-08-12 12:19 PM, 'Bo Jacoby' via Programming wrote:
```
```Don Guinn wrote: "But few things need precision beyond 16 significant digits".
Well, just computing the determinant of a 4*4 matrix of 4-figure integers require 16
digit precision!```
```
Den 1:52 lørdag den 12. august 2017 skrev Don Kelly <d...@shaw.ca>:
```
```  Right on!

In most numerical operations on a  computer, there is an inherent
propagation of errors (in fact Numerical analysis texts spend a lot of
effort on ways to reduce such errors) and 16 or more digits don't
provide precision greater than  that of the input data but do reduce the
computational  fuzz to an insignificant level. The ideal kit for a
student using a hand calculator would be a strip of electrical tape to
cover the extra digits.

Don Kelly

On 2017-08-11 6:33 AM, Don Guinn wrote:
```
```We too often assume that calculations carried out to 16 significant digits
are accurate when the input may not be known to less than 2 or 3
significant digits. We can calculate the distance to the moon accurately to
the wavelength of visible light in IEEE floating point. We can calculate
the national debt to the penny. Maybe calculating relativistic effects on a
satellite orbiting the earth might exceed IEEE floating point. But few
things need precision beyond 16 significant digits.

On Thu, Aug 10, 2017 at 11:14 PM, Don Kelly <d...@shaw.ca> wrote:

```
```isn't an advantage of APL and J that the person writing a
program/app/whatever, doesn't  have to deal with the distinctions between
integer and damn near integer  within the limitations of the computer
binary resolution?. In most cases this isa good thing because close enough
-given the +/- of data input is sufficient for the idiot box to decide. J
moves away from C/C++/ and other languages which often seem to be
emphasizing stuff that Iverson tried to eliminate in APL and J . Muh of
that stuff is something that can be handled by the idiot box so that:

Problem-->basic analysis--. coding that fits the analysis rather than the
details( users aim at the essentials rather than the details- "/I  want the
answer and I dont care about what is involved in the background of %,*
*/

The discussion below deals with representation of numeric values being
floating point or integer when pushing the limits-IS IT IMPORTANT IN THE
REAL WORLD unless  you have a Cray in the back bedroom?

Old fart expressing opinions

Don Kelly

On 2017-08-10 6:27 PM, Bill wrote:

```
```I suspect J interpreter didn't has the knowledge  that the original
with .3 because what J saw was the floating point result of parsing by c
library. Ieee floating point has 15 to 16 significant digits so that 1e16
and 1e16-1 is the same number.

Perhaps one could use long double to parse number on J64.

Sent from my iPhone

On 10 Aug, 2017, at 3:48 AM, Henry Rich <henryhr...@gmail.com> wrote:

Quite right.
```
```Henry Rich

On Aug 9, 2017 20:46, "Raul Miller" <rauldmil...@gmail.com> wrote:

Well, since it's encoded as an integer (which I would have noticed if
```
```I had read Bob Therriault's original post more closely), and not [like
I was thinking] a float, I agree that dropping the .3 is better than

That said, I guess we also should not object too loudly if
9999999999999999.3 were instead encoded the same as
9999999999999999+0.3 gets encoded.

Thanks,

--
Raul

On Wed, Aug 9, 2017 at 3:25 PM, Henry Rich <henryhr...@gmail.com>
wrote:

```
```Surely integer 999...9 is a better value than 1000...0 .

Henry Rich

On Aug 9, 2017 18:33, "Raul Miller" <rauldmil...@gmail.com> wrote:

It's not a bug, it's an artifact of the 64 bit floating point standard.
```
```     2 ^.9999999999999999
53.1508

https://en.wikipedia.org/wiki/IEEE_754#Basic_and_interchange_formats

The binary64 format has 53 binary digits or 15.95 decimal digits. This
means ".16#'9' cannot be represented exactly using this format.

And, we do not use exact representation of large numbers by default
because that's too slow for large datasets. Put differently, if you
want exact representation and are willing to take the performance hit,
you should specify that. For example: ".'x',~16#'9' or
".'3r10+','x',~16#'9'

Thanks,

--
Raul

On Wed, Aug 9, 2017 at 12:05 PM, Henry Rich <henryhr...@gmail.com>

```
```wrote:
This is a bug,  since 999...9.3 should become 999...9 rather than
```
```100...0.

```
```I'm away from home now,  but I think what's happening is this:

999...9 is converted to integer

. is encountered and turns it to float

It's rounded to the nearest float which is 100...0

As a final step the JE checks to see if the value is exactly
integral,
which it is,  and it is converted back to integer.

If you add this to Interpreter/Bugs I'll fix it when i get back.

Henry Rich

On Aug 9, 2017 16:16, "bill lam" <bbill....@gmail.com> wrote:

I think this is the difference between 32 and 64-bit,

9!:14''
j602/2008-03-03/16:45
3!:0[ 9999999999999999.3
4

In J32

a.i. 2 fc 9999999999999999.3
0 128 224 55 121 195 65 67
a.i. 2 fc 1e16
0 128 224 55 121 195 65 67

the number has the same bit pattern as 1e16 (an integer)
which can be represented as a 64-bit integer. I guess
J64 is correct since 9999999999999999.3 and 1e16 is the
same number in ieee fp and J prefers integer to floats,
eg
3!:0 [ 2.0
4

Ср, 09 авг 2017, robert therriault написал(а):

```
```Hi Pascal,

I see the same behaviour in j806 as j805. Do you see something

```
```different?
JVERSION
```
```Engine: j806/j64avx/darwin
Beta-4: commercial/2017-06-27T12:55:06
Library: 8.06.03
Qt IDE: 1.5.3/5.6.2
Platform: Darwin 64
Installer: J806 install
InstallPath: /users/bobtherriault/j64-806
Contact: www.jsoftware.com
(; datatype) 999999999999999.3
┌────┬────────┐
│1e15│floating│
└────┴────────┘
(; datatype) 9999999999999999.3
┌─────────────────┬───────┐
│10000000000000000│integer│
└─────────────────┴───────┘
(; datatype) 99999999999999999.3
┌──────────────────┬───────┐
│100000000000000000│integer│
└──────────────────┴───────┘
(; datatype) 999999999999999999.3
┌───────────────────┬───────┐
│1000000000000000000│integer│
└───────────────────┴───────┘
(; datatype) 9999999999999999999.3
┌────┬────────┐
│1e19│floating│
└────┴────────┘

Cheers, bob

On Aug 9, 2017, at 7:54 AM, 'Pascal Jasmin' via Programming <
programm...@jsoftware.com> wrote:
in j806,    9999999999999999.310000000000000000 probably the j805
behaviour is preferred.  If only for consistency.  But there may be
```
```a

```
```good

```
```reason for change.

```
```       From: robert therriault <bobtherria...@mac.com>
```
```To: Programming forum <programm...@jsoftware.com>
Sent: Wednesday, August 9, 2017 10:40 AM
Subject: [Jprogramming] Integer-floating type change for large

```
```numbers
```
```in j805 and j806
```
```I am guessing that the following has something to do with
precision of
```
```large numbers in j805 and is also true for j806.
```
```     (; datatype) 999999999999999.3
```
```┌────┬────────┐
│1e15│floating│
└────┴────────┘
(; datatype) 9999999999999999.3
┌─────────────────┬───────┐
│10000000000000000│integer│
└─────────────────┴───────┘
(; datatype) 99999999999999999.3
┌──────────────────┬───────┐
│100000000000000000│integer│
└──────────────────┴───────┘
(; datatype) 999999999999999999.3
┌───────────────────┬───────┐
│1000000000000000000│integer│
└───────────────────┴───────┘
(; datatype) 9999999999999999999.3
┌────┬────────┐
│1e19│floating│
└────┴────────┘
JVERSION
Engine: j805/j64/darwin
Release: commercial/2016-12-11T08:17:56
Library: 8.05.14
Qt IDE: 1.5.4/5.6.2
Platform: Darwin 64
Installer: J805 install
InstallPath: /applications/j64-805
Contact: www.jsoftware.com

Further investigation shows me it was not this way with the 32 bit

```
```version of j701, so it may be an artifact of moving to 64 bit?
(; datatype) 999999999999999.3
```
```┌────┬────────┐
│1e15│floating│
└────┴────────┘
(; datatype) 9999999999999999.3
┌────┬────────┐
│1e16│floating│
└────┴────────┘
(; datatype) 999999999999999999.3
┌────┬────────┐
│1e18│floating│
└────┴────────┘
(; datatype) 9999999999999999999.3
┌────┬────────┐
│1e19│floating│
└────┴────────┘
JVERSION
Engine: j701/2011-01-10/11:25
Library: 7.01.088
Platform: Darwin 32
Installer: j701a_mac_intel.dmg
InstallPath: /Applications/j701

Cheers, bob

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