Gaußverteilung

Gaußverteilung

Skalarer Fall (1D)

Eigenschaften Normalverteilung, Normalverteilung, Wendestellen, Standardabweichung, Varianz, Mittelwert, Sigma, MΓΌ, Maximum, Erwartungswert, Funktion Normalverteilung f(x)=12πσexp⁑{βˆ’12(xβˆ’x^)2Οƒ2} f(x)=\frac{1}{\sqrt{2 \pi} \sigma} \exp \left\{-\frac{1}{2} \frac{(x-\hat{x})^{2}}{\sigma^{2}}\right\}
  • Erwartungswert

    Ef{x}=x^ E_{f}\{x\}=\hat{x}
  • Varianz

    Ef{(xβˆ’x^)2}=Οƒ2 E_{f}\left\{(x-\hat{x})^{2}\right\}=\sigma^{2}

Given the parameters ΞΌ\mu and Οƒ\sigma of a Gaussian density, mean and variance are already given. On the other hand, assume that we wish to approximate a given density f~x\tilde{f}_x with a simpler density of the same mean and standard deviation. Then, given the mean and the standard deviation of the density f~x\tilde{f}_x, an appropriate Gaussian density is immediately obtained. This is a property not generally shared by more complicated densities.

2D Normalverteilung

fxy(x,y)=12πσxΟƒy1βˆ’r2exp⁑{βˆ’12Q(x,y)}Q(x,y)=11βˆ’r{(xβˆ’x^)2Οƒx2βˆ’2rxβˆ’x^Οƒxyβˆ’y^Οƒy+(yβˆ’y^)2Οƒy2} \begin{aligned} f_{x y}(x, y)&=\frac{1}{2 \pi \sigma_{x} \sigma_{y} \sqrt{1-r^{2}}} \exp \left\{-\frac{1}{2} Q(x, y)\right\} \\ Q(x, y)&=\frac{1}{1-r}\left\{\frac{(x-\hat{x})^{2}}{\sigma_{x}^{2}}-2 r \frac{x-\hat{x}}{\sigma_{x}} \frac{y-\hat{y}}{\sigma_{y}}+\frac{(y-\hat{y})^{2}}{\sigma_{y}^{2}}\right\} \end{aligned}
  • r∈[βˆ’1,1]r \in [-1, 1]: Korrelationskoeffizent (in some literature also written as ρ\rho)

Alternativ

fxy(x,y)=N([xy],[x^y^],[CxxCxyCyxCyy]) f_{x y}(x, y)=\mathcal{N} \left(\left[\begin{array}{l} x \\ y \end{array}\right],\left[\begin{array}{l} \hat{x} \\ \hat{y} \end{array}\right],\left[\begin{array}{ll} C_{x x} & C_{x y} \\ C_{y x} & C_{y y} \end{array}\right]\right)

mit

[cxxcxycyxcyy]=[σx2rσxσyrσxσyσy2] \left[\begin{array}{ll} c_{x x} & c_{x y} \\ c_{y x} & c_{y y} \end{array}\right]=\left[\begin{array}{lc} \sigma_{x}^{2} & r \sigma_{x} \sigma_{y} \\ r \sigma_{x} \sigma_{y} & \sigma_{y}^{2} \end{array}\right]

Correlationskoeffizient

Correlation of bivariate Gaussian distribution ($\rho$ is the correlation coefficient). (Source: 
)

Correlation of bivariate Gaussian distribution (ρ\rho is the correlation coefficient). (Source: )

  • unkorreliert (r=0r = 0) (Figure 1 right)

    • β‡’x,y\Rightarrow \boldsymbol{x}, \boldsymbol{y} unkorreliert
    • β‡’\Rightarrow (nur fΓΌr Gauß) x,y\boldsymbol{x}, \boldsymbol{y} unabhΓ€ngig (fx,y=fx(x)fy(y)f_{\boldsymbol{x}, \boldsymbol{y}} = f_{\boldsymbol{x}}(x) f_{\boldsymbol{y}}(y) )
  • positiv korreliert (r>0r > 0) (Figure 1 left)

  • positiv korreliert (r<0r < 0) (Figure 1 middle)

NN-dim. Normalverteilung

fx(x)=1(2Ο€)Nβ‹…βˆ£C∣exp⁑{βˆ’12(xβ€Ύβˆ’x^β€Ύ)⊀Cβˆ’1(xβ€Ύβˆ’x^β€Ύ)} f_{\boldsymbol{x}}(x)=\frac{1}{\sqrt{(2 \pi)^{N} \cdot|\mathbf{C}|}} \exp \left\{-\frac{1}{2}(\underline{x}-\underline{\hat{x}})^{\top} \mathbf{C}^{-1}(\underline{x}-\underline{\hat{x}})\right\}
  • x^β€Ύ\underline{\hat{x}} : Mean
  • C\mathbf{C} : Kovarianzmatrix