Multilayer perceptron questions

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In the discussion, the focus is on optimizing multilayer perceptrons in Matlab for image classification using adaptive learning with momentum backpropagation (traingdx). It is noted that lower initial learning rates yield better accuracy, while higher rates lead to a significant drop in model performance. This behavior can be attributed to the sensitivity of the model to learning rates, where excessive values may cause instability in training. Additionally, the impact of different output activation functions on model performance is explored. The user observes that certain configurations, such as {'tansig', 'tansig', 'purelin'} and {'tansig', 'tansig', 'tansig'}, perform well, while {'tansig', 'tansig', 'logsig'} fails, likely due to the logsig function zeroing out negative values. The discussion highlights the importance of both learning rate selection and the choice of activation functions, suggesting that experimentation may be necessary to find optimal configurations.
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So I am experimenting with different configurations of multilayer perceptrons in Matlab and my training data are extracted from images which I want to classify.

-I am currently using adaptive learning with momentum backpropagation (traingdx) setting different initial learning rates.What I get is that for low values I have a pretty good results but when the initial rate gets bigger the accuracy of my model drops dramatically.How can this be explained?

-Another question I have is how different output activation functions can affect your model.Are there some heuristics for this or just trial and error? For example I get good results with {'tansig', 'tansig', 'purelin'}, {'tansig', 'tansig', 'tansig'} but {'tansig', 'tansig', 'logsig'} fails, I suspect it has to do with negative values getting zeroed by logsig.
 
There is a discussion of learning rates in Sutskever's guest post on Yisong Yue's blog: http://yyue.blogspot.sg/2015/01/a-brief-overview-of-deep-learning.html
 
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