You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: nlp_prob.m
    path of file: ./repos/OPTI/Test Problems
    
    the code of the file until where you have to start completion: function [prob,sol,fmin] = nlp_prob(varargin)
%NLP_PROB  Return an OPTI NLP 
%
%   prob = nlp_prob(no) return a pre-built optiprob of a saved NLP.
%
%   [prob,sol,fmin] = nlp_prob(no) returns the optimum solution and 
%   function eval at the optimum
%
%   no = nlp_prob() returns the number of problems available for testing.
%
%   NOTE as implemented problems 1-50 return a Hock-Schittkowski
%   problem (see nlp_HS), while other numbers are other problems.

    
function [prob,sol,fmin] = nlp_prob(varargin)
%NLP_PROB  Return an OPTI NLP 
%
%   prob = nlp_prob(no) return a pre-built optiprob of a saved NLP.
%
%   [prob,sol,fmin] = nlp_prob(no) returns the optimum solution and 
%   function eval at the optimum
%
%   no = nlp_prob() returns the number of problems available for testing.
%
%   NOTE as implemented problems 1-50 return a Hock-Schittkowski
%   problem (see nlp_HS), while other numbers are other problems.

%   (C) 2011 Jonathan Currie (Control Engineering)

%Check if just returning no problems
if(nargin < 1)
    prob = 50; sol = []; fmin = [];
    return;
else
    no = varargin{1};
end