ENH: Added classes for neurons with tanh and arctan activation functions.

src/data_kinds_4neuro_m.f90

+#define SINGLE 4
+#define DOUBLE 8
+
+# define PREC DOUBLE
+
 module data_kinds_4neuro_m
-    integer, parameter :: integer_4neuro = 8
-    integer, parameter :: real_4neuro    = 8
+    integer, parameter :: integer_4neuro = PREC
+    integer, parameter :: real_4neuro    = PREC
 end module data_kinds_4neuro_m

src/neuron_m.f90

@@ -99,7 +99,6 @@ module neuron_m
 
         real(kind=real_4neuro) :: threshold  !< When neuron potential exceeds this value, neuron becomes excited
 
-
     contains
 
         !> Activation function - transforms potential into the output state value
@@ -132,8 +131,8 @@ module neuron_m
         private
 
         !! Coefficients for the linear activation function in format 'f(x)=a*x + b'
-        real(kind=real_4neuro) :: a_coef  !> The coefficient 'a' in the activation function f(x)=a*x + b
-        real(kind=real_4neuro) :: b_coef  !> The coefficient 'b' in the activation function f(x)=a*x + b
+        real(kind=real_4neuro) :: a_coef  !< The coefficient 'a' in the activation function f(x)=a*x + b
+        real(kind=real_4neuro) :: b_coef  !< The coefficient 'b' in the activation function f(x)=a*x + b
 
         contains
 
@@ -163,7 +162,7 @@ module neuron_m
     type, extends(neuron_t) :: logistic_neuron_t
         private 
 
-        real(kind=real_4neuro) :: alpha_coef
+        real(kind=real_4neuro) :: alpha_coef  !< The alpha coefficient used in the activation function
 
         contains
 
@@ -183,6 +182,38 @@ module neuron_m
         module procedure :: new_logistic_neuron_1
     end interface logistic_neuron_t
 
+    !---------------------!------------------------------------------------------------------------
+    ! class tanh_neuron_t !
+    !---------------------!
+
+    !> Hyperbolic tangent neuron class - uses f(x) = (e^x - e^(-x))/(e^x + e^(-x)) as 
+    !! an activation function, 'x' being the neuron potential.
+    type, extends(neuron_t) :: tanh_neuron_t
+        contains
+
+            !> Activation function - hyperbolic tangent
+            procedure, private :: activate => hyperbolic_tangent_activate_impl
+    end type tanh_neuron_t
+
+    interface tanh_neuron_t
+        !> Constructor for an instance of the class tanh_neuron_t
+        module procedure :: new_tanh_neuron
+    end interface tanh_neuron_t
+
+    !> Arcus tangents neuron class - uses f(x)=tan^(-1)(x) as an
+    !! activation function, 'x' being the neuron potential
+    type, extends(neuron_t) :: arctan_neuron_t
+        contains
+
+            !> Activation function - arcus tangens
+            procedure, private :: activate => arcus_tangens_activate_impl
+    end type arctan_neuron_t
+
+    interface arctan_neuron_t
+        !> Constructor for an instance of the class arctan_neuron_t
+        module procedure :: new_arctan_neuron
+    end interface arctan_neuron_t
+
     contains
         !------------------------!---------------------------------------------------------------------
         ! Method implementations !
@@ -567,5 +598,98 @@ module neuron_m
 #endif
         end subroutine logistic_activate_impl
 
+        !---------------------!
+        ! class tanh_neuron_t !
+        !---------------------!
+
+        !--------------!------------------------------------------------------------------------------
+        ! Constructors !
+        !--------------!
+
+        !> Constructor for an instance of the class tanh_neuron_t
+        function new_tanh_neuron() result(new_obj)
+            class(tanh_neuron_t), pointer :: new_obj
+#ifdef TIME_PROFILING
+            real                          :: start_time
+            call time_profiling_start(start_time)
+#endif
+
+            allocate(new_obj)
+            call new_obj%init_components()
+
+#ifdef TIME_PROFILING
+            call time_profiling_stop(start_time, 'new_tanh_neuron')
+#endif
+        end function new_tanh_neuron
+
+        !----------------!----------------------------------------------------------------------------
+        ! Common methods !
+        !----------------!
+
+        !> Activation function - hyperbolic tangent
+        subroutine hyperbolic_tangent_activate_impl(this)
+            class(tanh_neuron_t), intent(inout) :: this
+#ifdef TIME_PROFILING
+            real                                :: start_time
+            call time_profiling_start(start_time)
+#endif
+
+#if PREC == DOUBLE
+            this%state = dtanh(this%potential)
+#else
+            this%state = tanh(this%potential)
+#endif
+
+#ifdef TIME_PROFILING
+            call time_profiling_stop(start_time, 'hyperbolic_tangent_activate_impl')
+#endif
+        end subroutine hyperbolic_tangent_activate_impl
+
+        !-----------------------!
+        ! class arctan_neuron_t !
+        !-----------------------!
+
+        !--------------!------------------------------------------------------------------------------
+        ! Constructors !
+        !--------------!
+
+        !> Constructor for an instance of the class arctan_neuron_t
+        function new_arctan_neuron() result(new_obj)
+            class(arctan_neuron_t), pointer :: new_obj
+#ifdef TIME_PROFILING
+            real                          :: start_time
+            call time_profiling_start(start_time)
+#endif
+
+            allocate(new_obj)
+            call new_obj%init_components()
+
+#ifdef TIME_PROFILING
+            call time_profiling_stop(start_time, 'new_arctan_neuron')
+#endif
+        end function new_arctan_neuron
+
+        !----------------!----------------------------------------------------------------------------
+        ! Common methods !
+        !----------------!
+
+        !> Activation function - arcus tangens
+        subroutine arcus_tangens_activate_impl(this)
+            class(arctan_neuron_t), intent(inout) :: this
+#ifdef TIME_PROFILING
+            real                                  :: start_time
+            call time_profiling_start(start_time)
+#endif
+
+#if PREC == DOUBLE
+            this%state = datan(this%potential)
+#else
+            this%state = atan(this%potential)
+#endif
+
+#ifdef TIME_PROFILING
+            call time_profiling_stop(start_time, 'arcus_tangens_activate_impl')
+#endif
+        end subroutine arcus_tangens_activate_impl
 
 end module neuron_m