Added new lambda function class to enable passing of complex functions into the BFGS minimizer

Makefile

@@ -54,6 +54,7 @@ SWIFTEST_MODULES =   swiftest_globals.f90 \
                      module_swiftestalloc.f90 \
                      io.f90 \
                      module_interfaces.f90 \
+							lambda_function.f90\
                      swiftest.f90 
 
 include Makefile.Defines

src/modules/lambda_function.f90

@@ -0,0 +1,50 @@
+module lambda_function
+   !! Defines a class that can enable objects that behave like lambda functions.
+   use swiftest_globals
+   implicit none
+
+   type, public :: lambda_obj 
+      private
+      procedure(lambda0), pointer, nopass :: lambdaptr => null()
+   contains
+      generic   :: init => lambda_init_0
+      procedure :: eval => lambda_eval_0
+      procedure :: lambda_init_0
+   end type
+
+   abstract interface
+      function lambda0(x)
+         ! Template for a 0 argument function
+         import DP
+         real(DP), intent(in) :: x
+         real(DP) :: lambda
+      end function
+   end interface
+
+   contains
+      subroutine lambda_init_0(self, lambda)
+         implicit none
+         ! Arguments
+         class(lambda_obj), intent(out) :: self
+         procedure(lambda0)             :: lambda
+
+         self%lambdaptr => lambda
+      end subroutine lambda_init_0
+
+      function lambda_eval_0(self, x) result(y)
+         implicit none
+         ! Arguments
+         class(lambda_obj), intent(in) :: self
+         real(DP),          intent(in) :: x
+         ! Result
+         real(DP)                      :: y
+
+         if (associated(self%lambdaptr)) then
+            y = self%lambdaptr(x)
+         else
+            error stop "Initialize the object (call init) before computing values (call exec)!"
+         end if
+      end function lambda_eval_0
+
+end module lambda_function
+

src/modules/swiftest.f90

@@ -7,6 +7,7 @@ module swiftest
    use swiftest_data_structures
    use io
    use user
+   use lambda_function
    !$ use omp_lib
    implicit none
    public