Square Root Mapping  

Robert P. Munafo, 2002 May 17.

A transformation in which points are mapped onto new positions by the function

f(z) = C1 + C2 (z-C3)(1/2)

where C1, C2 and C3 are constants; usually C1=C3 and the absolute value of C2 is less than 1. Notice the symbol + indicating that the square root has two possible values — each point maps onto two new locations, positioned 180o apart from one another. Thus, if the mapping has been applied to an image, you get two distorted copies of the original image.

A close approximation to the square root mapping can be seen in the bifurcation in the filaments around islands. For example, when zooming in towards an island, there is an area of 2-fold symmetry, then further in you find an area of 4-fold symmetry. The inner area of 4-fold symmetry is very close to what you would get by taking the 2-fold symmetry features and applying a square root map with C1 = C3 equal to the coordinates of the island at the center and a C2 corresponding to the conbined rotation and size ratio between the 2-fold and the 4-fold features.

On his web page Quick Guide to the Mandelbrot Set, Paul Derbyshire sums it up pretty well with this description:

The familiar double spiral is another example of this phenomenon. Inside a seahorse spiral there is a mini Mandelbrot; near the mini Mandelbrot there are two spirals joined exactly at the point where the minibrot is. [...] [in these examples] the bottom image is invariably two of the top image joined at the marked point, sometimes in a convoluted fashion.

The square root mapping can also be applied in reverse (particularly useful when you have a mystery Mandelbrot image and want to find its coordinates); this reverse mapping is squaring.

From the Mandelbrot Set Glossary and Encyclopedia, by Robert Munafo, (c) 1987-2017.     Mu-ency index

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