diff options
Diffstat (limited to 'fg21sim/extragalactic')
| -rw-r--r-- | fg21sim/extragalactic/clusters/solver.py | 63 |
1 files changed, 49 insertions, 14 deletions
diff --git a/fg21sim/extragalactic/clusters/solver.py b/fg21sim/extragalactic/clusters/solver.py index 2f22f20..6c0e653 100644 --- a/fg21sim/extragalactic/clusters/solver.py +++ b/fg21sim/extragalactic/clusters/solver.py @@ -66,7 +66,7 @@ def TDMAsolver(a, b, c, d): class FokkerPlanckSolver: """ - Solve the Fokker-Planck equation. + Solve the Fokker-Planck equation: ∂u(x,t) ∂ / ∂u(x) \ u(x,t) ------- = -- | B(x)u(x) + C(x)----- | + Q(x,t) - ------ @@ -78,6 +78,30 @@ class FokkerPlanckSolver: Q(x,t) : injection coefficient (>=0) T(x,t) : escape coefficient + NOTE: The no-flux boundary condition is used. + + Parameters + ---------- + xmin, xmax : float + The minimum and maximum bounds of the X (spatial/momentum) axis. + x_np : int + Number of (logarithmic grid) points/cells along the X axis + tstep : float + Specify to use the constant time step for solving the equation. + f_advection : function + Function f(x,t) to calculate the advection coefficient B(x,t) + f_diffusion : function + Function f(x,t) to calculate the diffusion coefficient C(x,t) + f_injection : function + Function f(x,t) to calculate the injection coefficient Q(x,t) + f_escape : optional + Function f(x,t) to calculate the escape coefficient T(x,t) + buffer_np : int, optional + Number of grid points taking as the buffer region near the lower + boundary. The densities within this buffer region will be replaced + by extrapolating an power law to avoid unphysical accumulations. + This fix is ignored if this parameter is not specified. + References ---------- [1] Park & Petrosian 1996, ApJS, 103, 255 @@ -86,24 +110,18 @@ class FokkerPlanckSolver: http://adsabs.harvard.edu/abs/2014MNRAS.443.3564D """ - def __init__(self, xmin, xmax, grid_num, buffer_np, tstep, - f_advection, f_diffusion, f_injection, f_escape=None): + def __init__(self, xmin, xmax, x_np, tstep, + f_advection, f_diffusion, f_injection, + f_escape=None, buffer_np=None): self.xmin = xmin self.xmax = xmax - # Number of points on the logarithmic grid - self.grid_num = grid_num - # Number of grid points for the buffer region near the lower boundary - self.buffer_np = buffer_np - # Time step + self.x_np = x_np self.tstep = tstep - # Function f(x,t) to calculate the advection coefficient B(x,t) self.f_advection = f_advection - # Function f(x,t) to calculate the diffusion coefficient C(x,t) self.f_diffusion = f_diffusion - # Function f(x,t) to calculate the injection coefficient Q(x,t) self.f_injection = f_injection - # Function f(x,t) to calculate the escape coefficient T(x,t) self.f_escape = f_escape + self.buffer_np = buffer_np @property def x(self): @@ -111,7 +129,7 @@ class FokkerPlanckSolver: X values of the adopted logarithmic grid. """ grid = np.logspace(np.log10(self.xmin), np.log10(self.xmax), - num=self.grid_num) + num=self.x_np) return grid @property @@ -294,8 +312,15 @@ class FokkerPlanckSolver: distribution/spectrum and then extrapolate as a power law, in order to avoid the unphysical pile-up of electrons at the lower regime. + TODO: + Fit a power law to the same number (``buffer_np``) of data points, + then extrapolate it to fix the lower buffer region. + References: Ref.[2],Sec.(3.3) """ + if self.buffer_np is None: + return uc + uc = np.asarray(uc) x = self.x # Calculate the power-law index @@ -309,6 +334,14 @@ class FokkerPlanckSolver: uc[:self.buffer_np] = ya * (x[:self.buffer_np] / xa) ** s return uc + def time_step(self): + """ + Adaptively determine the time step for solving the equation. + + TODO/XXX + """ + pass + def solve_step(self, tc, uc): """ Solve the Fokker-Planck equation by a single step. @@ -334,7 +367,9 @@ class FokkerPlanckSolver: tc = tstart logger.info("Solving Fokker-Planck equation: " + "time: %.3f - %.3f" % (tstart, tstop)) - nstep = (tstop - tc) / self.tstep + nstep = int((tstop - tc) / self.tstep) + logger.info("Constant time step: %.3f (#%d steps)" % + (self.tstep, nstep)) i = 0 while tc < tstop: i += 1 |