I'm using the code from p480-481, the "Globally convergent newton method". After lnsrch is called, the "check" var will be set to false or true(which tells is lnsrch cannot give normal output). My problem is when it's checking if this is a spurious convergent by checking gradient of function, my output is really large, saying it's not spurious but still return with an invalid output. I'm pretty sure my input is smooth and should have solution. Can anyone tell me why lnsrch cannot make any progress and it's not a spurious convergence?