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links-own [ weight ] breed [ bias-nodes bias-node ] breed [ input-nodes input-node ] breed [ output-nodes output-node ] breed [ hidden-nodes hidden-node ] turtles-own [ activation ;; Determines the nodes output err ;; Used by backpropagation to feed error backwards ] globals [ epoch-error ;; measurement of how many training examples the network got wrong in the epoch input-node-1 ;; keep the input and output nodes input-node-2 ;; in global variables so we can output-node-1 ;; refer to them directly ] ;;; ;;; SETUP PROCEDURES ;;; to setup clear-all ask patches [ set pcolor gray ] set-default-shape bias-nodes "bias-node" set-default-shape input-nodes "circle" set-default-shape output-nodes "output-node" set-default-shape hidden-nodes "output-node" set-default-shape links "small-arrow-shape" setup-nodes setup-links propagate reset-ticks end to setup-nodes create-bias-nodes 1 [ setxy -6 14 ] ask bias-nodes [ set activation 1 set label activation set size 4] create-input-nodes 1 [ setxy -14 -6 set input-node-1 self set size 4 ] create-input-nodes 1 [ setxy -14 6 set input-node-2 self set size 4 ] ask input-nodes [ set activation random 2 set label (word "值为" activation) set label-color red] create-hidden-nodes 1 [ setxy 6 -6 ] create-hidden-nodes 1 [ setxy 6 6 ] ask hidden-nodes [ set activation random 2 set size 4 ] create-output-nodes 1 [ setxy 26 0 set output-node-1 self set activation random 2 set size 4 ] end to setup-links connect-all bias-nodes hidden-nodes connect-all bias-nodes output-nodes connect-all input-nodes hidden-nodes connect-all hidden-nodes output-nodes end to connect-all [ nodes1 nodes2 ] ask nodes1 [ create-links-to nodes2 [ set weight random-float 0.2 - 0.1 ] ] end to recolor ask turtles [ set color item (step activation) [ black white ] ] ask links [ set thickness 0.05 * abs weight ifelse show-weights? [ set label precision weight 4 ] [ set label "" ] ifelse weight > 0 [ set color [ 255 0 0 196 ] ] ; transparent red [ set color [ 0 0 255 196 ] ] ; transparent light blue ] end ;;; ;;; TRAINING PROCEDURES ;;; to train set epoch-error 0 repeat examples-per-epoch [ ask input-nodes [ set activation random 2 set label (word "值为" activation)] propagate backpropagate ] set epoch-error epoch-error / examples-per-epoch tick end ;;; ;;; FUNCTIONS TO LEARN ;;; to-report target-answer let a [ activation ] of input-node-1 = 1 let b [ activation ] of input-node-2 = 1 ;; run-result will interpret target-function as the appropriate boolean operator report ifelse-value run-result (word "a " target-function " b") [ 1 ] [ 0 ] end ;;; ;;; PROPAGATION PROCEDURES ;;; ;; carry out one calculation from beginning to end to propagate ask hidden-nodes [ set activation new-activation set label sigmoid sum [ [ activation ] of end1 * weight ] of my-in-links] ask output-nodes [ set activation new-activation set label sigmoid sum [ [ activation ] of end1 * weight ] of my-in-links] recolor end ;; Determine the activation of a node based on the activation of its input nodes to-report new-activation ;; node procedure report sigmoid sum [ [ activation ] of end1 * weight ] of my-in-links end ;; changes weights to correct for errors to backpropagate let example-error 0 let answer target-answer ask output-node-1 [ ;; `activation * (1 - activation)` is used because it is the ;; derivative of the sigmoid activation function. If we used a ;; different activation function, we would use its derivative. set err activation * (1 - activation) * (answer - activation) set example-error example-error + ((answer - activation) ^ 2) ] set epoch-error epoch-error + example-error ;; The hidden layer nodes are given error values adjusted appropriately for their ;; link weights ask hidden-nodes [ set err activation * (1 - activation) * sum [ weight * [ err ] of end2 ] of my-out-links ] ask links [ set weight weight + learning-rate * [ err ] of end2 * [ activation ] of end1 ] end ;;; ;;; MISC PROCEDURES ;;; ;; computes the sigmoid function given an input value and the weight on the link to-report sigmoid [input] report 1 / (1 + e ^ (- input)) end ;; computes the step function given an input value and the weight on the link to-report step [input] report ifelse-value input > 0.5 [ 1 ] [ 0 ] end ;;; ;;; TESTING PROCEDURES ;;; ;; test runs one instance and computes the output to test let result result-for-inputs input-1 input-2 let correct? ifelse-value result = target-answer [ "correct" ] [ "incorrect" ] user-message (word "The expected answer for " input-1 " " target-function " " input-2 " is " target-answer ".\n\n" "The network reported " result ", which is " correct? ".") end to-report result-for-inputs [n1 n2] ask input-node-1 [ set activation n1 ] ask input-node-2 [ set activation n2 ] propagate report step [ activation ] of one-of output-nodes end ; Copyright 2006 Uri Wilensky. ; See Info tab for full copyright and license.
There is only one version of this model, created 4 months ago by 彪 宋.
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