# The configuration file The **.conf** file contains different options which specify the problem that APM will solve. The contents of an example **.conf** file are shown below: ``` c_ref = 1 b_ref = 1 S_ref = 1 x_cg = 0 y_cg = 0 z_cg = 0 trailing_edge_angle = 150 p_ref = 101325 rho_ref = 1.225 mu_ref = 1.789e-5 norm_V_ref = 1 M_ref = 0 alpha = 0 beta = 0 p = 0 q = 0 r = 0 dt = 1 N_timesteps = 1 restart_from_checkpoint = 0 wake_alignment = 0 wake_angle = 0 wake_rollup = 1 output_frequency = 1 paraview_output = 1 tecplot_output = 0 json_output = 0 extended_output = 0 doublet_gradient_scheme = 0 neighbour_tolerance = 1e-6 trefftz_plane_analysis = 0 tip_panels = symmetry = 0 ``` {% hint style="info" %} The values in the above .conf file are in SI units - m, kg, s. You can use different units as long as they are consistent across the .conf file. {% endhint %} Refer to the table below for a detailed description of each option.

Option	Dimension	Description	Default value
Option	Dimensionality	Description	Default value
c_ref	L	Reference chord, used for non-dimensionalisation of the aerodynamic coefficients	1
b_ref	L	Reference span, used for non-dimensionalisation of the aerodynamic coefficients	1
S_ref	L^2	Reference area, used for non-dimensionalisation of the aerodynamic coefficients	1
x_cg, y_cg, z_cg	L	Location of the centre of gravity	0
trailing_edge_angle	-	Edges sharper than the trailing edge angle in degrees are identified as trailing edges	150
p_ref	M/(L{\cdot}T^2)	Reference pressure	101325
rho_ref	M/L^3	Reference density	1.225
mu_ref	M/(L{\cdot}T)	Reference dynamic viscosity	1.789e-5
norm_V_ref	L/T	Reference freestream speed	1
M_ref	-	Reference Mach number (used for compressibility corrections)	0
alpha, beta	-	Angle of attack and angle of sideslip with respect to the freestream in degrees	0
p, q, r	1/T	Roll, pitch, and yaw rates in degrees/sec	0
dt	T	Time step	1
N_timesteps	-	Number of timesteps	1
restart_from_checkpoint	-	Instructs the solver to restart the solution from a checkpoint	0
wake_alignment, wake_angle	-	Specifies how the wake aligns with respect to the trailing edges	0
wake_rollup	-	If disabled the induced velocities from the body on the wake and on the wake iteslf wont be calculated. The wake will be translated with the reference freestream speed.	1
json_output, paraview_output, tecplot_output	-	Enables or disables JSON, ParaView, and Tecplot output	0, 1, 0
extended_output	-	Appends force and moment vector for each panel in the Paraview and Tecplot output files	0
doublet_gradient_scheme	-	Instructs the solver how to calculate the doublet gradient	0
neighbour_tolerance	-	Specifies the neighbour tolerance criteria	1e-6
tip_panels	-	Instructs the solver to label specific panels as type 6	""
trefftz_plane_analysis	-	Performs trefftz analysis at the trefftz plane to evaluate lift and drag	0
symmetry	-	Enables symmetry across the x-y plane. The solutions 2x faster and the memory requirements are 2x lower.	0