title: How to solve a given optimization task with JOptimizer or any other Java library?
body: <p>I have got such an optimization problem:</p>
  
  <p>min a * x1^2 + b * x2^2 + c*x3^2 + d * x1*x2 + e * x1*x3 + f * x2*x3</p>
  
  <p>s.t. </p>
  
  <p>x1 + x2 + x3 + x4 = 1</p>
  
  <p>x1, x2, x3, x4 >= 0</p>
  
  <p>where a,b,c,d,e,f are given double type numbers</p>
  
  <p>Could you help me to solve it using a Java library (for example JOptimizer)? I have been trying to find something proper recently, but I didn't manage..</p>