Hi , I am working on some math stuff and I need to check some points ,
so are theses formulas correct ?

ISZ(x) : is it 0 ?

isz (x) = cos ( pi * ( (2*ceil( abs(x) ) + 1)) / 2 ) / cos(1)

Ins : Real number x

Out : 1 if x=0 , 0 if x <> 0

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SGN(x) : Sign

sgn(x) = abs(x) / ( x + isz(x) )

Ins : Real number x

Out : 1 if x>0 , 0 if x = 0 , -1 if x < 0
more here
Basic functions

thanks