# Cannot overfit on the IRIS dataset

I am playing with the IRIS dataset and want to see underfitting and overfitting in action. I am using a multilayer perceptron (2 layers).

It is pretty easy to underfit (see the plot below), but I am having problems with overfitting. The dataset capacity is 600 (# of samples (150) times # of features (4)), so I should be able to overfit using a network with a capacity bigger than that. I am trying to use a multilayer perceptron with a total # of parameters of ~32000, but overfitting does not happen. What is going on? Thank you!

If I make a learning rate smaller everything get smoother, but still no overfitting.

• Could you repost the plot, excluding the training lines? – jbowman Aug 24 '17 at 22:08
• For this type of analysis, you should be comparing a proper loss function like cross-entropy. Accuracy is necessarily limited to the set from 0 to 1 in fractions of $1/n$, so it will conceal considerable information about what's going on. – Sycorax Aug 24 '17 at 22:13
• @jbowman Sure, I added another plot. – Yuri Aug 24 '17 at 22:13
• Notice how, when you get out to epochs 50+, the purple line seems to give the poorest average result, followed by the turquoise (or whatever color that is) line, then it looks like the red is the next worst, which leaves the green as the best. @Sycorax is exactly correct, you should be using a proper loss function, but even with this accuracy measure you can, in an informal way, see a pattern there. – jbowman Aug 24 '17 at 22:16
• @jbowman But those are just some fluctuations, in the end all lines (except the blue one) are pretty close to each other. – Yuri Aug 24 '17 at 22:19