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c++eigenpow

Storing the absolute value of an eigen vector in to variable

I seem to have problem with a silly problem as storing a the absolute value of Eigen vector3d.

I want to compute the pow(p.cwiseAbs(),2) but since p.cwiseAbs() isn't a double, the function call doesn't work. i then tried to store it into a variable .. but somehow it doesn't seem possible..

ex.

double p_abs = p.cwiseAbs();

Error message: 

 error: cannot convert ‘const Eigen::CwiseUnaryOp<Eigen::internal::scalar_abs_op<double>, const Eigen::Matrix<double, 3, 1> >’ to ‘double’ in initialization
     double p_abs  = p.cwiseAbs();

How do i compute the pow(..,2) of the absolute value of the vector?.

The expression i am trying to write into code is :

The expression i am trying to code is the one explained by the first answer on this post.

https://math.stackexchange.com/questions/1784106/how-do-i-compute-the-closest-points-on-a-sphere-given-a-point-outside-the-sphere/1784159#1784159

Solution

  • To answer the original question "how-do-i-compute-the-closest-points-on-a-sphere-given-a-point-outside-the-sphere" using Eigen:

    Vector3d center, P, Q;
double radius;
Q = center + radius * (P-center).normalized()