How do I compute the absolute value of a vector in Eigen?

c++ eigen absolute-value
Reed Richards picture Reed Richards · Aug 16, 2014 · Viewed 12.5k times · Source

How do I compute the absolute value of a vector in Eigen? Since the obvious way

Eigen::VectorXf v(-1.0,-1.0,-1.0,-1.0,-1.0,-1.0,-1.0);
v.abs(); // Compute abs value.

does not work.

Answer

Reed Richards picture Reed Richards · Aug 16, 2014

For Eigen 3.2.1 using p.abs(); in the same way as you would use p.normalize results in a compiler error along the lines of

error: no member named 'abs' in 'Eigen::Matrix' p.abs(); ~ ^

so a vector in Eigen is nothing but a Matrix type. To compute the absolute values of a matrix in Eigen one can use p.cwiseAbs() or array conversion p.array().abs();. Both these absolute functions returns a value rather than modifying the variable itself.

So a correct way of doing it would be to do 

p = p.cwiseAbs();

or

p = p.array().abs();

Related questions

Initialise Eigen::vector with std::vector

I have seen it done before but I cannot remember how to efficiently initialize an Eigen::Vector of known length with a std::vector of the same length. Here is a good example: std::vector<double> v1 = {1.0, 2.0, 3.0}; Eigen::…

Read More
Euler to Quaternion / Quaternion to Euler using Eigen

I'm trying to implement a functionality that can convert an Euler angle into an Quaternion and back "YXZ"-convention using Eigen. Later this should be used to let the user give you Euler angles and rotate around as Quaternion and …

Read More
Convert Eigen Matrix to C array

The Eigen library can map existing memory into Eigen matrices. float array[3]; Map<Vector3f>(array, 3).fill(10); int data[4] = 1, 2, 3, 4; Matrix2i mat2x2(data); MatrixXi mat2x2 = Map<Matrix2i>(data); MatrixXi mat2x2 = Map<…

Read More