Of course, shortly after having sent this message I figured it out, but it
doesn't actually result in an increase in my throughput sadly. For
posterity:
#include <Eigen/Dense>
#include <iostream>
using namespace Eigen;
struct myUnaryFunctor {
const double m_base;
myUnaryFunctor(double base): m_base(base) {};
typedef double result_type;
result_type operator()(const int &e) const
{
return pow(m_base, e);
}
};
int main()
{
auto e = Eigen::ArrayXi::LinSpaced(11, 0, 10).eval();
double base = 2.9;
std::cout << e.unaryExpr(myUnaryFunctor(base));
}
On Mon, May 10, 2021 at 5:14 PM Ian Bell <[email protected]> wrote:
> I have a simple question that I have spent ages trying to work around over
> the years and still haven't found a satisfactory solution. I have a single
> double value, and without any allocation, I need to generate an Eigen
> expression that allows me to take a double to an array of integers. In my
> case, 25% of my code's execution time is spent working on this problem, and
> I think I should be able to get that contribution back to closer to zero.
> Initially I asked the question here:
> https://stackoverflow.com/questions/25354205/how-to-raise-double-to-array-powers-in-eigen
>
> This code doesn't compile (e.g., on godbolt):
>
> #include <Eigen/Dense>
>
> int main(){
> auto c = Eigen::ArrayXi::LinSpaced(11, 0, 10);
> auto r = Eigen::pow(3.7, c);
> }
>
> but if I switch the ArrayXi for ArrayXd it compiles (because the scalar
> types match), but that is not what I want.
>
> Really, what I need is to call my own implementation of pow(double, int),
> because it is MUCH faster than pow(double, double).
>
> In the end, I would like some guidance on how I can craft an Eigen
> expression for this use case that will not introduce any intermediate
> allocation.
>
> Thanks,
> Ian
>
