Question regarding while loop

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xxtan1
xxtan1 2020-8-16
编辑： Alan Stevens 2020-8-16
function y = approx_sqrt(x)
y = x;
while abs(y^2 - x) > 1e-7*x
y = (x/y + y)/2
This is part of the code in my lecture class. I wonder what is the purpose of setting y = x at the begining?
Can anyone explain to me? Thank you so much.
  1 个评论
KSSV
KSSV 2020-8-16
编辑：KSSV 2020-8-16
It is nothing but saving x into other vairable y. x is like an intital value; it is saved into y, there after value of y changes and gets updated.

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采纳的回答

Alan Stevens
Alan Stevens 2020-8-16
编辑：Alan Stevens 2020-8-16
(1) Because you need a value in the logic test: abs(y^2 - x) > ...
(2) Because you need an initial guess on the right-hand side of the Newton-Raphson expresssion: (x/y + y)/2

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