wip: A simple RNN example

Author: castelao

example/simple_rnn.f90

@@ -0,0 +1,48 @@
+program simple_rnn
+  use nf, only: dense, input, network, rnn, sgd
+  implicit none
+  type(network) :: net
+  real, allocatable :: x(:), y(:), p(:)
+  integer, parameter :: num_iterations = 1000
+  integer :: n, l
+
+  allocate(p(2))
+
+  print '("Simple RNN")'
+  print '(60("="))'
+
+  net = network([ &
+    input(3), &
+    rnn(5), &
+    rnn(1) &
+  ])
+
+  call net % print_info()
+
+  x = [0.2, 0.4, 0.6]
+  y = [0.123456, 0.246802]
+
+  do n = 0, num_iterations
+
+    do l = 1, size(net % layers)
+      if (net % layers(l) % name == 'rnn') call net % layers(l) % set_state()
+    end do
+
+    if (mod(n, 100) == 0) then
+      p(1:1) = net % predict(x)
+      p(2:2) = net % predict(x)
+      print '(i4,2(3x,f8.6))', n, p
+
+    else
+
+      call net % forward(x)
+      call net % backward(y(1:1))
+      call net % update(optimizer=sgd(learning_rate=.001))
+      call net % forward(x)
+      call net % backward(y(2:2))
+      call net % update(optimizer=sgd(learning_rate=.001))
+    end if
+
+  end do
+
+end program simple_rnn