How to solve a revised quadratic program problem

I need helps for solving the following quadratic maximum problem.

The quadprog(H, f, A, b) command is designed for solving:

subject to Ax<b.

However, my problem is described as follows:

subject to , where L=(1,1,...1) is the ones vector and k is negative constant.

It is kind of you to offer me the codes or an idea.

Thank you very much.

Answer 1

[Matt J]

Use fmincon. Be careful as well of the non-differentiability of the function at x=0. You should introduce a constraint that keeps it away from there.

[Matt J]

Wan-Yi Chiu's reply moved here:

Thank you very much.