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Christian Risi
2025-01-08 15:08:32 +01:00
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# Control Formulary
## Settling time
$
T_s = \frac{\ln(a_{\%})}{\zeta \omega_{n}}
$
- $\zeta$ := Damping ratio
- $\omega_{n}$ := Natural frequency
## Overshoot
$
\mu_{p}^{\%} = 100 e^{
\left(
\frac{- \zeta \pi}{\sqrt{1 - \zeta^{2}}}
\right)
}
$
## Reachable Space
$X_r = Span(K_c)$
$X = X_r \bigoplus X_{r}^{\perp} = X_r \bigoplus X_{nr}$
> [!TIP]
> Since $X_{nr} = X_r^{\perp}$ we can find a set of perpendicular
> vectors by finding $Ker(X_r^{T})$
## Non Observable Space
$X_no = Kern(K_o)$
$X = X_no \bigoplus X_{no}^{\perp} = X_no \bigoplus X_{o}$
> [!TIP]
> Since $X_{o} = X_no^{\perp}$ we can find a set of perpendicular
> vectors by finding $Ker(X_{no}^{T})$

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# Geometry Formulary
## Inverse of a Matrix
$A^{-1} = \frac{1}{det(A)} Adj(A)$
## Adjugate Matrix
The adjugate of a matrix $A$ is the `transpose` of the `cofactor matrix`:\
$Adj(A) = C^{T}$
### $(i-j)$-minor (AKA $M_{ij}$)
$M_{ij}$ := Determinant of the matrix $B$ got by removing the
***$i$-row*** and the ***$j$-column*** from matrix $A$
### Cofactors
$C$ is the matrix of `cofactors` of a matrix $A$ where all the elements $c_{ij}$
are defined like this:\
$
c_{ij} = \left( -1\right)^{i + j}M_{ij}
$
## Eigenvalues
By starting from the definition of `eigenvectors`:\
$A\vec{v} = \lambda\vec{v}$
As we can see, the vector $\vec{v}$ was unaffected by this matrix
multiplication appart from a scaling factor $\lambda$, called `eigenvalue`
By rewriting this formula we get:\
$
\left(A - \lambda I\right)\vec{v} = 0
$
This is solved for:\
$\det(A- \lambda I) = 0$
> [!NOTE]
> If the determinant is 0, then $(A - \lambda I )$ is not invertible, so
> we can't solve the previous equation by using the trivial solution (which
> can't be taken into account since $\vec{v}$ is not $0$ by definition)
## Caley-Hamilton
Each square matrix over a `commutative ring` satisfies its own
characteristic equation $det(\lambda I - A)$
> [!TIP]
> In other words, once found the characteristic equation, we can
> substitute the ***unknown*** variable $\lambda$ with the matrix itself
> (***known***),
> powered to the correspondent power

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# Physics Formulary
> [!TIP]
>
> You'll often see $\vec{v}$ and $\vec{\dot x}$, and $\vec{a}$ and
> $\vec{\ddot{x}}$.
>
> These are equal, but the latter forms, express better the relation
> between state space variables
## Hooke's Law (AKA Spring Formula)
$\vec{F} = -k\vec{x}$
- $k$: Spring Constant
- $\vec{x}$: vector of spring stretch from rest position
## Fluid drag
$\vec{F_D} = \frac{1}{2}b\vec{v}^2C_{D}A$
- $b$: density of fluid
- $v$: speed of object ***relative*** to the fluid
- $C_D$: drag coefficient
- $A$: cross section area
### Stokes Drag
$\vec{F_D} = -6 \pi R\mu \vec{v}$
- $\mu$: dynamic viscosity
- $R$: radius (in meters) of the sphere
- $\vec{v}$: flow velocity ***relative*** to the fluid
### Simplified Fluid Drag (Simplified Stokes Equation)
$\vec{F_D} = -b \vec{v}$
- $b$: simplified coefficient that has everything else
- $\vec{v}$: flow velocity ***relative*** to the fluid
##
## Newton force