optimget(o​ptions,'Pr​econdition​er',defaul​topt,'fast​');

Hello everybody, Could someone tell me what does exactly the recurrent line 'optimget(options,'****',defaultopt,'fast');' in the optimization toolbox files like lsqnonlin, for instance. '****' denoting any field that the optimization option can have. Especially, what is the role of the arguments: defaultopt and'fast' ? Many thanks in advance, Arnaud