Asked by Jack
on 2 Sep 2011

Hi all, please I need your help !

I've read all the posts here about Time Series Forecasting but still can't figure it out ! ** I'm drained**..

I've a **NARX** neural network with 10 hidden neurons and 2 delays. As input I have a 510x5 (called * Inputx*) and as output I have a 510x1 (called

I want to forecast 10 days ahead but it's really not working...

I tried the following code but I'm stuck now. **:-(**

Would you mind to help me ? **Some code will be awesome. :-(**

*******////////////////////////////////////////////******** *******/////////////////////////////////////////// **********

inputSeries = tonndata(Inputx,false,false);

targetSeries = tonndata(Target,false,false);

netc = closeloop(net);

netc.name = [net.name ' - Closed Loop'];

[xc,xic,aic,tc] = preparets(netc,inputSeries,{},targetSeries);

yc = netc(xc,xic,aic);

*******////////////////////////////////////////////******** *******/////////////////////////////////////////// **********

Answer by Lucas García
on 7 Sep 2011

Edited by Lucas García
on 3 Sep 2015

Accepted answer

Hi Jack,

When using `narxnet`, the network performs only a one-step ahead prediction after it has been trained. Therefore, you need to use `closeloop` to perform a multi-step-ahead prediction and turn the network into parallel configuration.

Take a look at this example for a multi-step-ahead prediction, *N* steps. This uses the dataset `magdata.mat` which is available in the Neural Network Toolbox. Also, some of the inputs will be used for performing the multi-step-ahead prediction, and results validated with the original data. I hope the comments help to understand.

*Edited in September 2015 to simplify step 5*

**%% 1. Importing data**

S = load('magdata');

X = con2seq(S.u);

T = con2seq(S.y);

**%% 2. Data preparation**

N = 300; % Multi-step ahead prediction

% Input and target series are divided in two groups of data: % 1st group: used to train the network

inputSeries = X(1:end-N);

targetSeries = T(1:end-N);

% 2nd group: this is the new data used for simulation. inputSeriesVal will % be used for predicting new targets. targetSeriesVal will be used for % network validation after prediction

inputSeriesVal = X(end-N+1:end);

targetSeriesVal = T(end-N+1:end); % This is generally not available

**%% 3. Network Architecture**

delay = 2;

neuronsHiddenLayer = 10;

% Network Creation net = narxnet(1:delay,1:delay,neuronsHiddenLayer);

**%% 4. Training the network**

[Xs,Xi,Ai,Ts] = preparets(net,inputSeries,{},targetSeries);

net = train(net,Xs,Ts,Xi,Ai);

view(net)

Y = net(Xs,Xi,Ai);

% Performance for the series-parallel implementation, only % one-step-ahead prediction perf = perform(net,Ts,Y);

**%% 5. Multi-step ahead prediction**

[Xs1,Xio,Aio] = preparets(net,inputSeries(1:end-delay),{},targetSeries(1:end-delay)); [Y1,Xfo,Afo] = net(Xs1,Xio,Aio);

[netc,Xic,Aic] = closeloop(net,Xfo,Afo); [yPred,Xfc,Afc] = netc(inputSeriesVal,Xic,Aic); multiStepPerformance = perform(net,yPred,targetSeriesVal);

view(netc)

figure;

plot([cell2mat(targetSeries),nan(1,N); nan(1,length(targetSeries)),cell2mat(yPred); nan(1,length(targetSeries)),cell2mat(targetSeriesVal)]')

legend('Original Targets','Network Predictions','Expected Outputs')

Show 7 older comments

phuong
on 28 Aug 2013

Greg Heath
on 30 Aug 2013

No need for a loop. The input and targets are time series, not single points from time series. Each step is performed automatically via sim or net.

When the loop is called,there is only the input series. The target series is replaced by output feedback.

Greg

Muhammad Azeem
on 17 Sep 2015 at 8:36

Answer by Mark Hudson Beale
on 9 Sep 2011

Here is an example that may help. A NARX network is trained on series inputs X and targets T, then the simulation is picked up at the end of X using continuation input data X2 with a closed loop network. The final states after open loop simulation with X are used as the initial states for closed loop simulation with X2.

% DESIGN NETWORK [x,t] = simplenarx_dataset; net = narxnet; [X,Xi,Ai,T] = preparets(net,x,{},t); net = train(net,X,T,Xi,Ai); view(net)

% SIMULATE NETWORK FOR ORIGINAL SERIES [Y,Xf,Af] = sim(net,X,Xi,Ai);

% CONTINUE SIMULATION FROM FINAL STATES XF & AF WITH ADDITIONAL % INPUT DATA USING CLOSED LOOP NETWORK.

% Closed Loop Network netc = closeloop(net); view(netc)

% 10 More Steps for the first (now only) input X2 = num2cell(rand(1,10));

% Initial input states for closed loop continuation will be the % first input's final states. Xi2 = Xf(1,:);

% Initial 2nd layer states for closed loop contination will be the % processed second input's final states. Initial 1st layer states % will be zeros, as they have no delays associated with them. Ai2 = cell2mat(Xf(2,:)); for i=1:length(net.inputs{1}.processFcns) fcn = net.inputs{i}.processFcns{i}; settings = net.inputs{i}.processSettings{i}; Ai2 = feval(fcn,'apply',Ai2,settings); end Ai2 = mat2cell([zeros(10,2); Ai2],[10 1],ones(1,2));

% Closed loop simulation on X2 continues from open loop state after X. Y2 = sim(netc,X2,Xi2,Ai2);

Show 1 older comment

Elma
on 18 Feb 2014

I have tried this code, and it is great, but when I try to apply it for my problem, I get really bad results. I tried with changing input and feedback delays, as well as number of hidden neurons, but the results are always bad (figure) (green line is multi step predistion)

The code is given below:

% DESIGN NETWORK ID=1:2; HL=6 FD=1:2;

net = narxnet(ID,FD,HL);

[X,Xi,Ai,T] = preparets(net,x,{},WS); net.divideFcn = 'divideblock'; net = train(net,X,T,Xi,Ai);

% SIMULATE NETWORK FOR ORIGINAL SERIES [Y,Xf,Af] = sim(net,X,Xi,Ai);

% CONTINUE SIMULATION FROM FINAL STATES XF & AF WITH ADDITIONAL % INPUT DATA USING CLOSED LOOP NETWORK.

% Closed Loop Network netc = closeloop(net);

Xi2 = Xf(1,:);

Ai2 = cell2mat(Xf(2,:)); for i=1:length(net.inputs{1}.processFcns) fcn = net.inputs{i}.processFcns{i}; settings = net.inputs{i}.processSettings{i}; Ai2 = feval(fcn,'apply',Ai2,settings); end Ai2 = mat2cell([zeros(10,2); Ai2],[10 1],ones(1,2));

Y2 = sim(netc,X2,Xi2,Ai2);

plot(1:length(WS),cell2mat(WS)) hold on plot(1:length(Y),cell2mat(Y),'r') plot(length(WS):length(WS)+length(Y2)-1,cell2mat(Y2),'g') legend('Input data - target series','One-step ahead prediction','Multi-step prediction beyond target series');

IOANNIS4
on 5 Aug 2015

Please can someone exlpain little bit more this part

% Xi2 = Xf(1,:); Ai2 = cell2mat(Xf(2,:)); for i=1:length(net.inputs{1}.processFcns) fcn = net.inputs{i}.processFcns{i}; settings = net.inputs{i}.processSettings{i}; Ai2 = feval(fcn,'apply',Ai2,settings); end Ai2 = mat2cell([zeros(10,2); Ai2],[10 1],ones(1,2)); Y2 = sim(netc,X2,Xi2,Ai2);

Please you would really help us, Kind regards, Ioannis

Answer by Greg Heath
on 25 Mar 2014

When the loop is closed, the net should be retrained with the original data and initial weights the same as the final weights of the openloop configuration.

Answer by mladen
on 25 Oct 2013

Be aware that predicting outputs this way (similar to cascade relaization of linear system) has great sensitivity to parametar estimation errors because they propagate in the process Mark Hudson Beale mentioned. This is highlighted in hard, multiple steps ahead problems.

Parallel realizations (simoltanoius output estimation...for instance 10 outputs of neural network for next 10 time steps) tend to be less sensitive to this errors. I have implemented this with my code which is alway prone to error :) So my subquestion is:

Is there some specific way to prepare my data for training with some matlab function?

Answer by Murat Akdag
on 28 Mar 2015

I'm trying to understand this narnet but still can't solve. Looking for help in matlab help section in this page: http://www.mathworks.com/help/nnet/ug/multistep-neural-network-prediction.html?searchHighlight=narnet%20multistep i try same codes but there is an error in >> [netc,xi,ai] = closeloop(net,xf,af); too many arguments. I just need one working sample about narnet which can predict 12 steps ahead prediction. I try to do with GUI in matlab NN section. But it has predict just 1 step ahead with removedelay command. I need 12 steps ahead. Thanks for help.

Greg Heath
on 17 Sep 2015 at 10:05

Your error message is because you are using an obsolete version. Try

netc = closeloop(net,xf,af);

Then find xi and ai from preparets

Hope this helps.

Greg

Answer by hugo kuribayashi
on 15 Apr 2015

Considering all this examples.. How can i calculate MAPE error instead MSE?

Opportunities for recent engineering grads.

## 2 Comments

## Oleg Komarov (view profile)

Direct link to this comment:http://es.mathworks.com/matlabcentral/answers/14970#comment_33198

Two things,please change the title of your post in something useful and format the code: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup#answer_18099

## Constantine (view profile)

Direct link to this comment:http://es.mathworks.com/matlabcentral/answers/14970#comment_250932

with respect to the accepted answer by Lucas Garcia, I find the predicted data only agrees with the actual data as well as his every once in a while.

1. It's important, before running the fit, to clear the variables, eg. 'clear all.' Re-running without clearing the variables leads to much worse fits.

2. much better fits result from using a bigger delay, like 5, instead of the delay of 2 in his example. Or by adding additional training data, such as the time derivative or 2nd time derivatives of the training data. Of course, doing this makes the fit considerably slower.