Math 2.0

Systems theory; control Problem

Linear-quadratic-Gaussian control

Builds on Linear-quadratic regulatorWiener processStochastic differential equationPositive semidefinite matrixPositive definite matrixExpected valueFiltration

Problem

Let AA, BB, CC be real matrices of sizes n×nn \times n, n×mn \times m and k×nk \times n, and let T>0T > 0. Let Q,FQ, F be symmetric positive semidefinite n×nn \times n matrices, and let RR be a symmetric positive definite m×mm \times m matrix. Let WW and VV be independent Wiener processes in ℝn\R^n and ℝk\R^k with covariance matrices Ξt\Xi t and Θt\Theta t. Here Ξ\Xi is positive semidefinite and Θ\Theta is positive definite. Let the initial state x(0)x(0) be Gaussian with mean m0m_0 and covariance Σ0\Sigma_0, independent of WW and VV. The state xx and the observation yy solve the stochastic differential equations dx=(Ax+Bu) dt+dW,dy=Cx dt+dV,y(0)=0.dx = (A x + B u) \, dt + dW, \qquad dy = C x \, dt + dV, \qquad y(0) = 0. A control is admissible if u(t)u(t) depends only on the observations y(s)y(s), s≤ts \le t, that is, uu is adapted to the filtration generated by yy. The linear-quadratic-Gaussian control problem is to minimize the expected value J(u)=𝔼[∫0T(xTQx+uTRu) dt+x(T)TFx(T)]J(u) = \mathbb{E}\Big[ \int_0^T \big( x^{T} Q x + u^{T} R u \big) \, dt + x(T)^{T} F x(T) \Big] over all admissible controls uu.

Remarks

The problem is solved, and its solution is the separation principle. The optimal control is u=−R−1BTP(t)x^(t)u = -R^{-1} B^{T} P(t) \hat{x}(t), where PP solves the Riccati equation of the linear-quadratic regulator and x^(t)\hat{x}(t) is the Kalman–Bucy filter estimate of x(t)x(t) from the observations. Without noise and with full observation of the state, the problem reduces to the linear-quadratic regulator. The infinite-horizon version uses the average cost per unit time and the algebraic Riccati equations of the regulator and of the filter. LQG controllers can have poor robustness margins, which was one motivation for robust control methods.

Reading path

To understand this page from the ground up, read these 11 pages in order. The foundations come first.

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Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
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  1. Algebraic Riccati equation concept
  2. Expected value concept
  3. Filtration concept
  4. Optimal control concept
  5. Positive definite matrix concept
  6. Positive semidefinite matrix concept
  7. Riccati differential equation of optimal control concept
  8. Stochastic differential equation concept
  9. Wiener process concept
  10. Linear-quadratic regulator problem
  11. Linear-quadratic-Gaussian control problem

Where this leads

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Further reading

  1. Web https://en.wikipedia.org/wiki/Linear–quadratic–Gaussian_control
About this page
TagDJB8MAV5BH
URIm2://DJB8MAV5BH
Kindproblem
WritingW0 stub
MSC93E20, 49N10, 93E11
StatusThis copy of the site has no build data. Run m2 status DJB8MAV5BH.
AboutLinear-quadratic regulator
UsesLinear-quadratic regulator, Wiener process, Stochastic differential equation, Positive semidefinite matrix, Positive definite matrix, Expected value, Filtration
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