relative error between a real and complex number.

[Pacopag]

1. The problem statement, all variables and given/known data
So I've got a polynomial with real roots. It turns out that if you perturb one of the coefficients by a small amount, two of the roots end up in the complex plane. Now I want to find the relative error in my computation. For two real numbers, say x1 and x2, I would take
rel.err. = {{x1-x2}\over{x1}}.
But what do I do if x1 is real and x2 is complex?


2. Relevant equations



3. The attempt at a solution

[olgranpappy]

1. The problem statement, all variables and given/known data
So I've got a polynomial with real roots. It turns out that if you perturb one of the coefficients by a small amount, two of the roots end up in the complex plane. Now I want to find the relative error in my computation. For two real numbers, say x1 and x2, I would take
rel.err. = {{x1-x2}\over{x1}}.
But what do I do if x1 is real and x2 is complex?


2. Relevant equations



3. The attempt at a solution

mabye try

\frac{|x_1-x_2|}{x_1}

[Pacopag]

Yes. That makes sense. It is the distance between the two values. Works in the complex plane too. Thanks.