title: PCA inverse transform manually
body: <p>I am using scikit-learn. The nature of my application is such that I do the fitting offline, and then can only use the resulting coefficients online(on the fly), to manually calculate various objectives.</p>
  
  <p>The transform is simple, it is just <code>data * pca.components_</code>, i.e. simple dot product. However, I have no idea how to perform the inverse transform. Which field of the <code>pca</code> object contains the relevant coefficients for the inverse transform? How do I calculate the inverse transform?</p>
  
  <p>Specifically, I am referring to the PCA.inverse_transform() method call available in the <code>sklearn.decomposition.PCA package</code>: how can I manually reproduce its functionality using various coefficients calculated by the PCA?</p>