The graph you made of the error function in Linear Regression looks like that of a paraboloid. I’m having difficulties in understanding how you made that graph. I found out from the equation for it to be of type
whereas what you drew was this:https://www.google.co.in/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiQhNOoicXcAhWIwI8KHfQHDXwQjRx6BAgBEAU&url=http%3A%2F%2Fwww.matrixlab-examples.com%2Fsimple-animation-3d.html&psig=AOvVaw2wQ115L0uFE8qdJ_tSqYVa&ust=1532979350916818