# multiply the point by 2^-1 (mod n)

Public key x and y == Double(Half of the Public key x and y)
how to code this in sage math how to get coordinate x

x = f9308a019258c31049344f85f89d5229b531c845836f99b08601f113bce036f9
y = 388f7b0f632de8140fe337e62a37f3566500a99934c2231b6cb9fd7584b8e672

from this to > x = c62c910e502cb615a27c58512b6cc2c94f5742f76cb3d12ec993400a3695d413 y = 17f3dadd767275ddd3b23f46723631778bf01dadaebb9a953cf068712457c010

I don't understand your question, can you rephrase it? What is happening to x and what is happening to y? What is n? Halving and then doubling sounds like it would do nothing.