I have three questions regarding the difference between a closed-loop and an open-loop narxnet, and it's behavior.
First, a little about the problem I'm trying to solve. I have an 2xN dimensional matrix of observation (X), from which I'm trying to predict an output Y, 1xN. Now, a narxnet takes as input both X and Y. The Matlab documentation says that an open-loop narxnet finds a function 'f' where y(t) = f( y(t-1), y(t-2), x(t-1), x(t-2) ), for a delay of 2. However, the results that I get are much more accurate than I expect them to be. This suggests that the narxnet uses the actual y(t) as input as well. When I convert the open-loop to a closed-loop, and retrain it, I get much more reasonable results, not good, but reasonable.
1.a) What is the actual input to an open-loop narxnet, and the closed-loop. When trying to predict y(t), are the inputs [ y(t), y(t-1), y(t-2), x(t-1), x(t-2) ] or [ y(t-1), y(t-2), x(t-1), x(t-2) ], for both?
1.b) For my problem I need the inputs to be [ y(t-1), y(t-2), x(t), x(t-1), x(t-2) ], 0 to 2 delays on the X, and 1 to 2 delays on the Y. How can I do that?
2. For comparison, I've trained my open-loop, and tested it, then convert the open-loop to a closed-loop using
netc = closeloop(net);
then trained the closed-loop from scratch and tested it. I've read on MATLAB Answers that I should start training the closed-loop with the weights from the open-loop net. How can I used the weights of one net as the initial weights for training another?
3. I understand that the narxnet uses a combination of NNs and difference equations. I problem I run into when using a closed-loop narxnet is that my predictions begin to oscillate and explode exponential. I know that this problem occurs in a difference equation, such as y(t)=a*y(t-1)+b, when 'a' is greater than 1. What, in a closed-loop narxnet could cause this similar issue?
I didn't include any code because my questions need high-level understanding and explanations, which I am lacking.
ANSWER
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% NARXNET closed-loop vs open-loop
% Asked by Yevgeniy Arabadzhi
% 8:38 PM Thursday, November 3, 2016
%
% I have three questions regarding the difference between
% a closed-loop and an open-loop narxnet, and it's behavior.
%
% First, a little about the problem I'm trying to solve. I
% have an 2xN dimensional matrix of observation (X), from
% which I'm trying to predict an output Y, 1xN. Now, a
% narxnet takes as input both X and Y. The Matlab
% documentation says that an open-loop narxnet finds a
% function 'f' where y(t) = f( y(t-1), y(t-2), x(t-1),
% x(t-2) ), for a delay of 2.
What you are overlooking is the role of the target; In fact, you never mention the target!The target is used to design and operate the OL net. To emphasize this point I prefer to use the following notation: Uppercase for cells
Lowercase for doubles and integers
X,x for inputs
T,t for targets
Y,y for outputs
i,j for timestep indices
% However, the results that I % get are much more accurate than I expect them to be. % This suggests that the narxnet uses the actual y(t) % as input as well. ABSOLUTELY NOT! You just happened to have an easy problem (which you did not identify!). There are a variety of sample datasets in the help and doc documentations. Use the commands help nndatasets
doc nndatsets
% When I convert the open-loop to a closed-loop, and retrain it, % I get much more reasonable results, not good, but reasonable.
Matlabsolutions.com provide latest MatLab Homework Help,MatLab Assignment Help for students, engineers and researchers in Multiple Branches like ECE, EEE, CSE, Mechanical, Civil with 100% output.Matlab Code for B.E, B.Tech,M.E,M.Tech, Ph.D. Scholars with 100% privacy guaranteed. Get MATLAB projects with source code for your learning and research.
% NARXNET closed-loop vs open-loop % Asked by Yevgeniy Arabadzhi % 8:38 PM Thursday, November 3, 2016 % % I have three questions regarding the difference between % a closed-loop and an open-loop narxnet, and it's behavior. % % First, a little about the problem I'm trying to solve. I % have an 2xN dimensional matrix of observation (X), from % which I'm trying to predict an output Y, 1xN. Now, a % narxnet takes as input both X and Y. The Matlab % documentation says that an open-loop narxnet finds a % function 'f' where y(t) = f( y(t-1), y(t-2), x(t-1), % x(t-2) ), for a delay of 2.
What you are overlooking is the role of the target; In fact, you never mention the target!
The target is used to design and operate the OL net. To emphasize this point I prefer to use the following notation:
Uppercase for cells Lowercase for doubles and integers X,x for inputs T,t for targets Y,y for outputs i,j for timestep indices
% However, the results that I % get are much more accurate than I expect them to be. % This suggests that the narxnet uses the actual y(t) % as input as well.
ABSOLUTELY NOT! You just happened to have an easy problem (which you did not identify!). There are a variety of sample datasets in the help and doc documentations. Use the commands
help nndatasets doc nndatsets
% When I convert the open-loop to a closed-loop, and retrain it, % I get much more reasonable results, not good, but reasonable.
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