Implement "double sqrt(double x)" in C++.

Question

Seckin · Accepted Answer

here is the code:

#include

double sq(double x){
    double mx = 32000;
    double mn = 0;
    while(mx - mn > 1e-9){
        double md = (mx + mn) / 2;
        if(md * md > x)
            mx = md;
        else
            mn = md;
    }
    return mx;
}
int main(){
    while(1){
        double db;
        scanf("%lf",&db);
        printf("%lf
",sq(db));
    }
}

Dah · Answer

Would it be more efficient in some cases to also check md*md == x?

Anonymous · Answer

Seckin's algorithm is correct (it is called binary search) but it not very efficient.
it will get you on average one bit of precision for each iteration.
the babylonian method will double the number of correct bits at each iteration.
It can be found here:
http://en.wikipedia.org/wiki/Methods_of_computing_square_roots

Dmitry · Answer

Algorithm above is partially correct since it would not give results for "0 < x < 1"

bellpeace · Answer

Here is my contribution:

double sq(double x){
    
		double sqr = 0;
		double offset = 1;

		while (1)
		{
			if (sqr*sqr == x)
			{
				break;
			}
			else if (sqr*sqr  > x){
				
				sqr -= offset;
				offset /= 10;
			}
			
			sqr += offset;
		}

		return sqr;

}

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