title: How can I know whether the cost function has become the minimum or not?
body: <p>I'm trying to implement logistic regression without using ML related libraries, and having trouble optimizing the cost function.</p>
  
  <p>I stored the history of cost function during the iteration.</p>
  
  <p>At first, the cost function started with the value of 0.68, and it decreased to about 0.66, then increased since then, becoming even higher than the initial cost function.</p>
  
  <p>Does this mean that I'm having some errors in my code?</p>
  
  <p>Or, can 0.66 be the minimum of the cost function?</p>
  
  <p>How can I know that the current cost function value is the minimum?</p>