Multifunctions: Two Branch Points


We have already seen a multifunction. It is the case of the cubic root that has three values and the point z=0 is called a branch point. Fractional powers are multifunctions. Now we are considering the twovalued multifunction We can draw a path on the left panel and see how this path is transformed on the right panel. If z travels along a closed loop like in this picture, not encircling any of the two branch points, its image f(z) travels along a closed loop and returns to its original value. However, if z instead travels along a closed loop which goes round only one of the branch points, then f(z) does not return to its original value but instead ends up at a different value of the multifunction. Similarly, if z travels along a closed loop encircling one of the branch points twice, then f(z) returns to its original value again. The same happens if the closed loop goes round both branch points.
REFERENCES
Tristan Needham  Visual Complex Analysis. (pag. 96)  Oxford University Press
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Complex power functions with natural exponent have a zero (or root) of multiplicity n in the origin.
A polynomial of degree 2 has two zeros or roots. In this representation you can see Cassini ovals and a lemniscate.
The Complex Cosine Function extends the Real Cosine Function to the complex plane. It is a periodic function that shares several properties with his real ancestor.
Inversion is a plane transformation that transform straight lines and circles in straight lines and circles.
Inversion preserves the magnitud of angles but the sense is reversed. Orthogonal circles are mapped into orthogonal circles
The complex exponential function is periodic. His power series converges everywhere in the complex plane.
