What does the ellipse in Gradient descent describes? I saw multiple articles describes GD or SGD with the following diagram:

I didn't saw any explanation about the ellipses.

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*What does each ellipse describe ?

*What is the meaning if the ellipse has large or small diameter ?

*Does the wights (which are the ellipse in the image) must has the ellipse shape ? (Are there any other shapes you can show as an example) ?


The ellipses are contours where the loss function is constant. This type of plot is usually known as "contour plot". The shape of ellipses is due to the loss surface, and any other shape could be possible.
