# Nomenclature

This page should serve as a guide to all the mathematical and physical symbols found in this documentation.

**Physical symbols**

| Symbol| Meaning|
| ------ | ------ |
|$T$ | Temperature [K]|
|$\lambda$ | Heat conductivity [W m$^{-1}$ K$^{-1}$]
|$\rho$ | Density [kg m$^{-3}$]|
|$c$ | Specific heat capacity [J kg$^{-1}$ K$^{-1}$]|
|$\Delta t$ | The time step size [s]|
|$\Delta x$ | The size of the volume around a discretized spatial point [m]|
|$\delta x$ | The distance between two discretized spacial points [m]|
|$Q_{\text{sol}}$ | The incoming solar power per area, usually time and angle dependent [W m$^{-2}$]|
|$Q_{\text{refl}}$ | The fraction of power per area gained by a surface through absorption of reflected light from surrounding geometry [W m$^{-2}$]|
|$Q_{\text{refl, total}}$ | The fraction of power per area gained by a surface through absorption of reflected light from surrounding geometry, altered for an incident angle dependent albedo case [W m$^{-2}$]|
|$Q_{\text{refl}}$ | The fraction of power per area gained by a surface through absorption of infrared thermal emission from surrounding geometry [W m$^{-2}$]|
|$\epsilon$ | Emissivity|
|$\sigma$ | Stefan-Boltzmann constant [W m$^{-2}$ K$^{-4}$]|
|$\alpha$ | Bond albedo|
|$\boldsymbol{x}$ | A coordinate vector of a point - in the context of facets the centroid|
|$F(\boldsymbol{x}_i \boldsymbol{x}_j)$| Viewfactor between facets|
|$\boldsymbol{F}_{ij}$ or $\boldsymbol{F}(\boldsymbol{x}_i \boldsymbol{x}_j)$ | Viewfactor matrix whose entries are the viewfactors scaled by the areas of the facets|


**Common abbreviations and namings**

| Abbreviation/Name| Meaning|
| ------ | ------ |
|TPM | Thermophysical model|
|GMRES | Generalized Minimum Residual Method|
|TDMA or Thomas-Algorithm | Tridiagonal Matrix Algorithm
|Facet | A polygonal surface element (most commonly a triangel or rectangle) of a bigger surface|
|Mesh | A collection of facets that describe a bigger surface, often containing information like vertices, facets, areas of facet, etc.|
|Tri/Tris | Shortform for Triangular polygon/trigon|