Engineering domain: Structure Design

## Task Description

Design domain is bounded by following vertices (-1,-1), (1,-1), (1,1), (-1,1). 
A sharp pre-crack is present in the domain, along the line (0,0) to (0,1). 
Horizontal loads are applied at (-1,1) along -ve x-axis and at (1,1) along +ve x-axis. 

The filter radius is R = 0.03*max(Lx,Ly).
The filter exponent is 3.


---

### Task

Your task is to:
- Design a structure that has minimum value of maximum stress such that volume fraction does not exceed 0.25.
- Given the optimized design, output the corresponding maximum stress, named s_hat, and also its volume fraction, named vf, in numerical numbers. Note that vf is in the range of [0,1].