Coefficient-wise custom functions in Eigen

c++, eigen

Solution

You can use `unaryExpr`, though this returns a new view onto the matrix, rather than allowing you to modify the elements in place.

Copying the example out of the documentation:

double ramp(double x)
{
  if (x > 0)
    return x;
  else 
    return 0;
}
int main(int, char**)
{
  Matrix4d m1 = Matrix4d::Random();
  cout << m1 << endl << "becomes: " << endl << m1.unaryExpr(ptr_fun(ramp)) << endl;
  return 0;
}

Problem

I have a `do_magic` method which takes a double and adds 42 to it. I'd like to apply this method to each coefficient of a `Eigen::Matrix` or `Eigen::Array` (that means, I wouldn't mind if it's only possible with one of both types). Is this possible? Like this: ``` Eigen::MatrixXd m(2, 2); m << 1,2,1,2; m.applyCoefficientWise(do_magic); // m is now 43, 44, 43, 44 ```

Original source