Question about logistic regression cost plot in C1_W3_Lab06_Gradient_Descent_Soln

One thing I couldn’t understand about the plot below: why does the chart show log(Cost(w,b)) instead of just Cost(w,b)? Doesn’t the logistic regression cost function already use logarithms?

The reason for using log of something in charts is to reduce the scale of the numbers in the graph so we can get visually a better understanding of what happens. This would normally be done when the values associated with each axis differ a lot in magnitude.

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Without log scaling the contour plot would look like this:

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It is a convenience for visualization.

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