title: Keras: how to record validation loss
body: <p>Note: this is a <a href="https://stackoverflow.com/questions/37664783/how-to-plot-a-learning-curve-for-a-keras-experiment">duplicate question</a>, but I'm not looking for the answer. Rather, how better to find the answer myself. </p>
  
  <p>How do I record loss, training accuracy, testing loss and testing accuracy, from a model, across epochs? I'd like to plot a graph that shows validation loss against each epoch.</p>
  
  <p>I know that the <a href="https://keras.io/callbacks/" rel="nofollow noreferrer">callback</a> object, which can be called in fit(), or maybe model.history has something to do with it, but examining the source and docstrings are just a wall of code to me. Numpy, for instance, typically provides a very small use case as an example of very simple implementation. And yet I know that the answer to this is just a one-liner, because this really is just a question of input.</p>