TheRedshiftRider 5, problem with zoom?

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Offline julofi

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« on: May 08, 2018, 02:35:52 PM »
Hi
I made a fractal some days ago with the version 2.13-2 of KF and I tried again today with the version 2.13-3 and when I zoom the fractal deeper than e015 the image gets completely pixeled.
I don't know if that is the normal behaviour or it is some bug. I include the parameters.
The formula used in the fractal is TheRedshiftRider 5.
Thanks.

Offline claude

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« Reply #1 on: May 08, 2018, 03:28:29 PM »
It's a bug, but one I'm not sure how to fix (and I think it's been there since the start - the pixelation already occurs in my first 2.11+gmp version): the problem is a combination of the formula az^2-z^4+c with a=1 and the location c near 1+0i : there is a catastropic cancellation when subtracting z^2-z^4 because both values are near 1, or at least that's what i think is happening.  It's fundamentally (1 + z)(1-z)z^2 so there will be issues when z is near +/- 1, which happens on the second iteration when c is near +/- 1 (when using seed 0).  Perturbation deals with z near a reference z, and I don't think it'd be simple to take account of additional constants too...

Sorry, I think you're out of luck :(

Offline julofi

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« Reply #2 on: May 08, 2018, 03:42:32 PM »
So it is a bug and very difficult to fix. Thanks for the explanation although Igot lost after the first sentence  :))
KF is a great piece of software anyway, so congratulations =) and thanks again.

Offline RedshiftRider

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« Reply #3 on: May 09, 2018, 06:59:43 AM »
Even in the non gmp kalles fraktaler it would also occur in specific areas. Back when the formulae were implemented I think, Karl told me that the formulae were going to be much slower than the others and that most attempts to speed it up would result in precision issues.

Offline Kalles Fraktaler

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« Reply #4 on: May 09, 2018, 01:32:16 PM »
Yes, there are some limitations in perturbation unfortunately, as Claude explained it.


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