Thanks for filling us in! I wouldn't think the animations themselves
would need such precision, though perhaps the calculations of the forces
and motions do. One way to check might be to perturb the initial
conditions a bit and see if the changes in the motions seem to be
correspondingly small. That might help you work out if the problem is
with the physics solution or the animation. It would be easy to get
some numerical instability in the calculations, for example if you are
inverting matrices.
On 12/18/2022 2:00 PM, Paul St George wrote:
So I am working on a physics paper with a colleague. We have a theory about
Newtons Cradle. We answer the question why when you lift and drop balls 1 and
2, balls 4 and 5 rise up. I could say more, but ... (if you are interested
please write to me).
We want to illustrate the paper with animations. The theory includes distortion
of the balls and this distortion is very very small. So, I am sent data with
locations and dimensions to 13 decimal places. Something strange is happening
with the animations: the balls are not moving smoothly. I do not know (yet)
where the problem lies so it is difficult to provide a clear narrative.
Because there is a problem, I am investigating in all areas. This brings me to
the question I asked here. I am not expecting six decimal places or three
decimal places to be as accurate as thirteen decimal places, but I would like
to be in control of or fully aware of what goes on under the bonnet.
Here is a picture:
https://paulstgeorge.com/newton/cyclography.html
Thanks,
Paul
On 17 Dec 2022, at 16:54:05 EST 2022, Thomas Passin wrote:
On 12/17/2022 3:45 PM, Paul St George wrote:
Thanks to all!
It was the rounding rounding error that I needed to avoid (as Peter J. Holzer
suggested). The use of decimal solved it and just in time. I was about to
truncate the number, get each of the characters from the string mantissa, and
then do something like this:
64550.727
64550 + (7 * 0.1) + (2 * 0.01) + (7 * 0.001)
Now I do not need to!
And that approach would not have helped you, because each of those
calculations would be done as floating point, and you wouldn't have
gotten any more precision (and maybe less) than simply doing
float('64550.727').
Here is a small but interesting discussion thread about float vs Decimal:
https://stackoverflow.com/questions/32053647/comparing-python-decimals-created-from-float-and-string
Would you mind telling us why that degree of precision (that is, decimal
vs float) matters for your problem?
On 17 Dec 2022, at 13:11, Alan Gauld <learn2program at gmail.com
<https://mail.python.org/mailman/listinfo/python-list>> wrote:
On 17/12/2022 11:51, Paul St George wrote:
I have a large/long array of numbers in an external file. The numbers look like
this:
-64550.727
-64511.489
-64393.637
-64196.763
-63920.2
When I bring the numbers into my code, they are Strings. To use the
numbers in my code, I want to change the Strings to Float type
because the code will not work with Strings but I do not want
to change the numbers in any other way.
That may be impossible. Float type is not exact and the conversion
will be the closest binary representation of your decimal number.
It will be very close but it may be slightly different when you
print it, for example. (You can usually deal with that by using
string formatting features.)
Another option is to use the decimal numeric type. That has other
compromises associated with it but, if retaining absolute decimal
accuracy is your primary goal, it might suit you better.
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
--
https://mail.python.org/mailman/listinfo/python-list
