Add loss-based stopping criterion and line search to GradientBasedSolver

[dwmunster]

Overview

Replaces the static step size with the Wolfe condition based line search for GradientBasedSolver. This typically leads to much larger accepted steps and faster convergence. This allows the GradientBasedSolver to successfully complete the CirclesWithLines benchmark even faster than BFGS, though it still fails for the largest StairsWithLines cases.

Benchmarks

From benchmark2:

Benchmark: CirclesWithLines
n:   30,        primitives:   59,       constraints:  88,       solver: GradientBasedSolver,    solved: true,   error: 0.00,    duration: 2ms
n:   30,        primitives:   59,       constraints:  88,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 1ms
n:   50,        primitives:   99,       constraints: 148,       solver: GradientBasedSolver,    solved: true,   error: 0.00,    duration: 3ms
n:   50,        primitives:   99,       constraints: 148,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 2ms
n:  100,        primitives:  199,       constraints: 298,       solver: GradientBasedSolver,    solved: true,   error: 0.00,    duration: 6ms
n:  100,        primitives:  199,       constraints: 298,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 7ms
n:  300,        primitives:  599,       constraints: 898,       solver: GradientBasedSolver,    solved: true,   error: 0.00,    duration: 16ms
n:  300,        primitives:  599,       constraints: 898,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 51ms
Benchmark: StairsWithLines
n:   30,        primitives:   59,       constraints:  59,       solver: GradientBasedSolver,    solved: false,  error: 0.00,    duration: 63ms
n:   30,        primitives:   59,       constraints:  59,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 0ms
n:   50,        primitives:   99,       constraints:  99,       solver: GradientBasedSolver,    solved: false,  error: 0.00,    duration: 97ms
n:   50,        primitives:   99,       constraints:  99,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 1ms
n:  100,        primitives:  199,       constraints: 199,       solver: GradientBasedSolver,    solved: false,  error: 1.10,    duration: 188ms
n:  100,        primitives:  199,       constraints: 199,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 10ms
n:  300,        primitives:  599,       constraints: 599,       solver: GradientBasedSolver,    solved: false,  error: 29.68,   duration: 555ms
n:  300,        primitives:  599,       constraints: 599,       solver: BFGSSolver         ,    solved: true,   error: 0.00,    duration: 246ms