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C++ atan2 Function

The C++ Valarray::atan2() function calculates the inverse tangent of the (y/x) value of each element in the valarray and returns a valarray containing the inverse tangent of all the items. where y is the proportion of the y-coordinate and x is the proportion of the x-coordinate.

The atan2() function of cmath is overload with in this function, which calls it once for each element. It uses the sings of the arguments to determine the appropriate quadrant.

• If both the y,x are of same valarray size,the function computes the inverse of the each pair of corresponding values from y and x.
• If y is valarray and x is value, the function computes the inverse tangent of each element of y paired with x.
• If x is valarray and y is value, the function computes the inverse tangent of y paired with each element of x.

Following is the syntax for C++ Valarray::atan2 Function −

atan2 (const valarray<T>& y, const valarray<T>& x);
atan2 (const valarray<T>& y, const T& x);
atan2 (const T& y, const valarray<T>& x);

• x − It is containing elements of a type for which the unary function abs is defined.
• y − It is a valarray element with the y coordinate(s).

Let's look into the following example, where we are going to use atan2() function and retrieving the output.

#include <iostream>
#include <valarray>
using namespace std;

int main() {
   double y[] = { 0.4, 1.2, -1.0 };
   double x[] = { 0.5, 1.3, -1.0 };
   valarray<double> ycoords(y, 2);
   valarray<double> xcoords(x, 2);
   valarray<double> result = atan2(ycoords, xcoords);
   cout << "Result:";
   
   for (size_t i = 0; i < result.size(); ++i)
      cout << ' ' << result[i];
   cout << '\n';
   return 0;
}

Let us compile and run the above program, this will produce the following result −

Result: 0.674741 0.745419

Considering the another scenario, where we are going to use the atan2() function and retrieving the output.

#include <iostream>
#include <valarray>
using namespace std;

int main (){
   valarray<double> y = {4, 10, 9};
   valarray<double> x = {12, 22, 14};
   valarray<double> result1 = atan2(y, x);
   cout<<"\natan2(y, x) returns: ";
   
   for(int i = 0; i < result1.size(); i++)
      cout<<result1[i]<<" ";  
   return 0;
}

Let us compile and run the above program, this will produce the following result −

atan2(y, x) Return: 0.321751 0.426627 0.571337  

In the following example, we are going to use atan2() function and retrieving the output in radians.

#include <iostream>
#include <cmath>
#define PI 3.141592654
using namespace std;

int main() {
   double result;
   int x = -12;
   float y = 31.6;
   result = atan2(y, x);
   cout << "atan2(y/x) = " << result << " radians" << endl;
   return 0;
}

Let us compile and run the above program, this will produce the following result −

atan2(y/x) = 1.93372 radians

Following is the example, where we are going to use atan2() function and retrieving the output in degrees.

#include <iostream>
#include <cmath>
#define PI 3.141592654
using namespace std;

int main() {
   double result;
   int x = -12;
   float y = 31.6;
   result = atan2(y, x);
   cout << "atan2(y/x) = " << result * (180 / PI) << " degrees";
   return 0;
}

Let us compile and run the above program, this will produce the following result −

atan2(y/x) = 110.794 degrees

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