DEEP NEURAL NETWORKS FOR MODELING NONLINEAR DYNAMICS

A comparison of Shannon's cross entropy and mean squared error ... Squared Error (MSE) vs Cross Entropy. (CE) ... 5 repetitions of 10-fold cross validation. 1. 1.
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D EEP N EURAL N ETWORKS FOR M ODELING N ONLINEAR D YNAMICS

A comparison of Shannon‘s cross entropy and mean squared error N AJEEB K HAN AND I AN S TAVNESS D EPARTMENT OF C OMPUTER S CIENCE , U NIVERSITY OF S ASKATCHEWAN . I NTRODUCTION

R ESULTS

• Evaluation metric: root mean squared error (RMSE) • 5 repetitions of 10-fold cross validation

• Arm reaching movements can be modeled as a mapping [1]

Dataset partitioned into k folds 1 1

Joint Space

test

5 6

Torque trajectory

Hidden features α

Y-axis

Elbow Angle θ2

0

0.2

7 0 −0.2

−2

−1

0

1

2

3

Shoulder Angle θ1

−0.4 −0.8 −0.6 −0.4 −0.2

0

0.2

0.4

0.6

0.8

X-axis

test test test

Input features α

Hidden features β

Hidden features α

Hidden features β

Initial and final states

Reconstructed trajectory

Hidden layer α

Hidden layer β

6

#10

τˆ1

τˆ1

α1

α ˆ1

τ2

τˆ2

τˆ2

τˆ3

α2

α ˆ2

τ3

τˆ3

τˆ3

τ4

τˆ4

α3

α ˆ3

τ4

τˆ4

χ1

τˆ4

τ5

τˆ5

α4

α ˆ4

τ5

τˆ5

χ2

τˆ5

τ6

τˆ6

α5

α ˆ5

τ6

τˆ6

τˆ6

τ7

τˆ7

α6

α ˆ6

τ7

τˆ7

τˆ7

τ8

τˆ8

τ8

τˆ8

τˆ8

τ2

τˆ2

τ3

(a) Learning hidden features α from torque trajectory

(b) Learning hidden features β from hidden features α

100

200

300

α ˆ1

α2

α ˆ2

α3

α ˆ3

α4

α ˆ4

α5

α ˆ5

α6

α ˆ6

400

500

Cross Entropy Mean Squared Error

τ1

τˆ1

τ2

τˆ2

τ3

τˆ3

τ4

τˆ4

τ5

τˆ5

τ6

τˆ6

τ7

τˆ7

τ8

τˆ8

5 4 3 2 1

#10!3

6

200

300

400

(c) Pre-training a deep autoencoder

·10−3 4

τ1

τˆ1

τ2

τˆ2

τ3

τˆ3

τ4

τˆ4

τ5

τˆ5

τ6

τˆ6

τ7

τˆ7

τ8

τˆ8

CE MSE

(d) Deep network predicting torque trajectory from initail and final state

·10−2

τˆ7

τ8

τˆ8

100

200

300

400

·10−3

α1

α ˆ1

α2

α ˆ2

α3

α ˆ3

α4

α ˆ4

α6

RMSE

τˆ6

τ7

1

CE MSE

7

α ˆ5 α ˆ6

1.2

6

1

5

0.8

500

τ1

τˆ1

τ2

τˆ2

τ3

τˆ3

τ4

τˆ4

τ5