Reformulated Neural Network (ReNN) A New Alternative for Data-driven Modelling in Hydrology and Water Resources Engineering Saman Razavi 1, Bryan Tolson

Reformulated Neural Network (ReNN)

A New Alternative for Data-driven Modelling in Hydrology and Water Resources Engineering

Saman Razavi1, Bryan Tolson1, Donald Burn1, and Frank Seglenieks2

1 Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada

2 Environment Canada, Burlington, Ontario, Canada

Outline of the Presentation

Introduction to Reformulated Neural Network

Application 1 – Metamodelling

Application 2 – Rainfall-Runoff Modelling

A new Measure of Regularization

Summary

2

ReNN is:– Essentially a single-hidden-layer

neural network– Defined on a new set of

variables based on the network’s internal geometry

x1

Input Layer Output LayerHidden Layer

x2

xR

y

Iw1,1

Iw1,2

Iw1,

R

Iw2,1Iw2,2

Iw2,R

Iwn,1

Iwn,2

Iwn,R

Hw1

Hw2

Hw n

Ob

Hb1

Hb2

Hbn

Ho1

Ho2

Hon

Main Features:– ReNN is more efficient in training– ReNN variables are interpretable– ReNN is more predictable in

generalization

Reformulated Neural NetworkMultilayer Perceptron (Traditional Neural Network)

3

y

Ob

Iw1,1

Iwn,1

Hw1

Hw n

Hb1

Hbn

Ho1

Hon 1

-1.5

-1.25

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

1.25

1.5

-1.5 -1.25 -1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1 1.25 1.5

Out

put

Input

Hw

i .H

o i

x1

Hwi .Hoix1


Iwi,1 Hwi

Hbi

Hoi

Height

Location

Slope

Hwi

di = -Hbi / Iwi,1

si = Hwi . Iwi,1

Reformulated Neural Network

ReNN variables in 1-input problems

4

a sigmoidal unit

y

Ob

Hb1

Hbn

Ho1

Hon

x1


x2

Iwi,1

Iwi,2Hwi

Hbi

Hoi

x1

x2

Hw

1 Ho 1 Height

Location

Angle

SlopeDirectional

Slopes

Height

Location &

Slope

Angle

New Variables:

Directional Slope 1

Directional Slope 2

Reformulated Neural Network

ReNN variables in 2-input problems

5

Details include: Generalized geometry & revised neural network formulation with respect to the new variablesDerive the partial derivatives of the network error function with respect to the new variables for back-propagation training algorithms

Razavi, S., and Tolson, B. A. (2011). "A new formulation for feedforward neural networks." IEEE Transactions on Neural Networks, 22(10), 1588-1598, DOI: 1510.1109/TNN.2011.2163169.

ReNN in n-input problems is non-trivial but for details see Razavi and Tolson (2011)

Example Applications …

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0

0.04

0.08

0.12

0.16

0.2

0 1000 2000 3000 4000 5000

Mea

n Sq

uare

d E

rror

Epoch

ANN 2-10-1 ReNN 2-10-1

Test FunctionSWAT2000 Hydrologic ModelCannonsville Reservoir Watershed, NY

Saving

ReNN Efficiency in Training - Case Study 1

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 500 1000 1500 2000 2500

Mea

n Sq

uare

d E

rror

Epoch

ANN 14-10-1 ReNN 14-10-1

Example Application in MetamodellingNeural networks are frequently used to model (emulate) computationally expensive models (e.g., in optimization, model calibration, real-time/ operational settings)

Network Training efficiency is very important.

Averaged over 50 trials

Averaged over 50 trials

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trained with Standard Back-propagation Alg. trained with Standard Back-propagation Alg.

Precipitation Gauge 1(t)




Average Precipitation (t-1)

Average Temperature (t)

Runoff (t)ReNN6-5-1

Interpretation of ReNN Variables – Case Study 2

Precipitation Gauge 3

WaltonRunoff Gauge




Cannonsville Reservoir Watershed New York (area = 1200 km2)

Example Application in Rainfall-Runoff Modelling(monthly)

Input-output data are scaled to [-1 +1]

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Sigmoidal Unit 1 0.62

Sigmoidal Unit 2 -0.04




25.92

-1.42

8.70

-6.60

-17.55

-0.05

0.25

-0.02

-2.65

-0.68

HeightsOverall Slopes Locations Output Bias

8.56-8.30 -5.72 -6.70 -4.16 -22.14 4.25

0.52 0.55 0.69 0.07 -0.74 -0.65

3.43 1.77 2.62 1.53 6.76 -2.44

1.39 2.61 -1.31 -0.80 5.46 1.65

1.30 1.85 2.41 1.93 -14.95 -5.07


WaltonRunoff Gauge





PR1(t) PR2(t) PR3(t) PR4(t) PR (t-1) TP(t)Directional Slopes

16-16

1

-1

0.8


9






25.92

-1.42

8.70

-6.60

-17.55

-0.05

0.25

-0.02

-2.65

-0.68

HeightsOverall Slopes Locations Output Bias

8.56-8.30 -5.72 -6.70 -4.16 -22.14 4.25

0.52 0.55 0.69 0.07 -0.74 -0.65

3.43 1.77 2.62 1.53 6.76 -2.44

1.39 2.61 -1.31 -0.80 5.46 1.65

1.30 1.85 2.41 1.93 -14.95 -5.07


WaltonRunoff Gauge





PR1(t) PR2(t) PR3(t) PR4(t) PR (t-1) TP(t)Directional Slopes

8.65

8.56

Output Bias

2.65


10

16-16

1

-1

regnew =

Performance function with regularization:

Conventional measure of regularization:

regconventional =

Performance Function = * mse + * regneww (1 - w)

ReNN Regularization Measure

This measure directly quantifies the smoothness of the network response.

Among two networks with the same accuracy on the training data, the one with smoother response (more regularized) is expected to have better generalizability

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This measure is applicable to both ReNN and traditional neural networks

Summary


Reformulated Neural Network (ReNN) is an equivalent reformulation of multilayer perceptron (MLP) neural networks with the following benefits:

ReNN is trained faster,

ReNN has an interpretable Internal Geometry – e.g. useful for Sensitivity Analysis, and

ReNN has a direct measure of regularization (smoothness).

ReNN can turn into traditional neural network.

For full information on ReNN formulation and derivations, please refer to:

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For full information on ReNN formulation and derivations, please refer to:

Thank You

Documents

Reformulated Neural Network (ReNN) A New Alternative for Data-driven Modelling in Hydrology and Water Resources Engineering Saman Razavi 1, Bryan Tolson