Re: zero point of secp256k1

Quote from: mausuv on Today at 06:58:54 AM

solve this please

Code:

example input: # + and - mixed
-3942323
56456
-3
-342
-33398
683

Code:

output : #always positive value
3942323
56456
3
342
33398
683

i know abs() method returns the absolute value of a number and √(x^2) = all value positive

i need math steps
example:
https://www.wolframalpha.com/input/?i=3942323%2F-1+*++-1
https://www.wolframalpha.com/input/?i=-3942323%2F-1+*++-1

√(x^2) = only rootsqure alternative method maths explain please #mybad english

I'm not sure what you are asking me to solve but in modular arithmetic we aren't arbitrarily changing the sign of a negative number to positive. Instead the congruent number is computed.
For example if the modulus is 7 then -1 becomes 6 or -9 becomes 5.
Essentially we compute (a mod m) then if the result was negative we add modulus to the result.

Code:

-9%7=-2 -> -2+7=5 -> -9 ≡ -2 ≡ 5 (mod 7)

As for square root, it is also different in modular arithmetic. You have to compute r so that r²≡a (mod 9).
For secp256k1 curve we have a simple solution to compute ModPow(a, (p+1)/4, p) but in general cases where p%4 != 3 we have to use an algorithm like Tonelli–Shanks.