Lambdas

Simple example

#include <FMath/Core>

using FMath::Field;
using FMath::scalar;

Field<scalar> sf(5, 0.0);

auto lambda = [](std::size_t i, scalar& val)
{
    // Every value of the field is set to a calculated value
    val = i+5;
};

sf.apply_lambda(lambda);

// Example entries of `sf`
// sf[0] == 5
// sf[3] == 8

Complex example

This example shows a reasonably complex calculation:

1. each entry of intermediate should contain the sum of its “neighbours” in orientations
2. each entry of res should contain the scalar product of said sum with orientations

As should be, the first operation (in form of a lambda) and the second will be performed in parallel over the elements of the result Field.

#include <FMath/Core>

using FMath::Field;
using FMath::scalar;
using FMath::Vector3;

int N = 5;
std::vector<int> relative_indices({-1,+1});
Field<Vector3> orientations(N, Vector3{0,0,1});
Field<Vector3> intermediate(N, Vector3{0,0,0});
Field<scalar> res(N, 0.0);

auto lambda = [&](std::size_t idx, Vector3& val)
{
    // Inside entries get both directions
    if( idx > 0 && idx < orientations.size()-1 )
    {
        for( auto& rel : relative_indices )
        {
            val += orientations[idx+rel];
        }
    }
    // Left end: right-hand side
    else if( idx == 0 )
        val += orientations[idx+1];
    // Right end: left-hand side
    else if( idx == orientations.size()-1 )
        val += orientations[idx-1];
};

// Result: scalar field of products of vectors in `orientations` and `intermediate`
res = orientations.dot(intermediate.applied_lambda(lambda));

// Contents of result:
// res[0] == 1
// res[1] == 2
// res[2] == 2
// res[3] == 2
// res[4] == 1