ForTimize

General API for optimizing routines

Motivation

Fortran has a huge ecosystem in optimization libraries, but they are dispersed with different APIs and different ways to define objective functions. This library aims to standarize the way to call optimization functions to ease the process of selecting algorithms to optimize problems.

Disclaimer

This is still a prototype project so big changes can happen

Examples

For examples of usage check the examples directory.

Objective function definition.

The objective function that should be minimized must have the following interface

module my_objective
    use ForTimize, only: pr

contains

    subroutine foo(X, F, dF, data)
        real(pr), intent(in) :: x(:)
            !! Vector of parameters to optimize
        real(pr), intent(out) :: F 
            !! Value of the objetive function after optimization.
        real(pr), optional, intent(out) :: dF(:) !!
            !! Optional gradient.
        class(*), optional, intent(in out) :: data
            !! Special data that the function could use.

        F = sum(x+2)**2
    end subroutine
end module

Then the objective function can be optimized with:

program main
    use ForTimize, only: pr, minimize
    use my_objective, only: foo

    real(pr) :: x(3), F

    ! Initial guess
    x = [1, 2, 5]

    ! Minimize uses the Nelder-Mead algorithm as a default    
    call minimize(foo, x, F)
    
    ! Print results
    print *, x
    print *, F
end program

How to include new algorithms

All the optimization algorithms should extend the Abstract type Optimizer, which ensures that the optimize method is respected.

module my_new_optimizer
    use ForTimize__constants, only: pr
    use ForTimize__core, only: Optimizer, objective_function

    type, extends(Optimizer) :: MyNewAlgorithm
    contains
        procedure :: optimize => optimizer_implementation
    end type

contains

    subroutine optimizer_implementation(self, foo, X, F, data)
        class(Optimizer), intent(in out) :: self 
            !! Optimizer object
        procedure(objective_function) :: foo 
            !! Objective function to minimize
        real(pr), intent(in out) :: X(:) 
            !! Vector of parameters
        real(pr), intent(out) :: F 
            !! Function value after optimization
        class(*), optional, target, intent(in out) :: data 
            !! Optional data that could be useful for the function

        ! Optimizer procedures here.
    end subroutine