Probably a math function problem


I write code for solving a 2nd-degree equation, and I get this error

IncrementalExecutor::executeFunction: symbol '_ZSt3absd' unresolved while linking [cling interface function]!
You are probably missing the definition of std::abs(double)
Maybe you need to load the corresponding shared library?

what shared library I need to load?
ROOT Version: 6
Platform: Linux

#include <cmath>

Thanks. I used it but error still remained!

This is my code:

		       Double_t b = - 2*pzv;
		       Double_t c = Mw*Mw - El*El - Ev*Ev + pxl*pxl + pxv*pxv + pyl*pyl + pyv*pyv + pzl*pzl - 2*El*Ev - 2*pxl*pxv - 2*pyl*pyv;
		       Double_t delta = b*b - 4*a*c;
		       Double_t x1 = (-b + sqrt(delta))/2;
		       Double_t x2 = (-b - sqrt(delta))/2;

		       if (delta > 0){

			 if (abs(x1) > abs(x2)){

			 pzv = x2;
			   pzv = x1;

Try also to: #include <cstdlib>