<p>This can be dealt with by enabling the <code>hydro</code> parameter in the <code>RUN_PARAMS</code> section of the namelist file.</p>

CC BY-SA 4.0
2023-01-23T22:10:25.113Z
2023-01-23T22:10:25.113Z
BooleanDesigns
<p>I am working on setting up N-body simulations of galaxy mergers. The initial conditions are generated from the DICE code, and looking at them, they seem very realistic. Unfortunately, when I let RAMSES run, it fails to converge. The output looks something like this</p>
<pre><code>Initial mesh structure
 Level  1 has          1 grids (       0,       1,       0,)
 Level  2 has          8 grids (       4,       4,       4,)
 Level  3 has         64 grids (      32,      32,      32,)
 Level  4 has        512 grids (     256,     256,     256,)
 Level  5 has       4096 grids (    2048,    2048,    2048,)
 Level  6 has      32768 grids (   16384,   16384,   16384,)
 Level  7 has     262144 grids (  131072,  131072,  131072,)
 Starting time integration
 Load balancing AMR grid...
   ==&gt; Level=    7 Step=   10 Error=       NaN
 WARN: Fine multigrid Poisson failed to converge...
 Fine step=      0 t= 0.00000E+00 dt= 2.714E+04 a= 1.000E+00 mem=17.3%  0.0%
 Time elapsed since last coarse step:    5.76 s        5.50 mus/pt        5.50 mus/pt (av)
 Used memory:    799.9 MB
 Total running time:   97.1599960     s
   ==&gt; Level=    7 Step=   10 Error=       NaN
 WARN: Fine multigrid Poisson failed to converge...
 Mesh structure
 Level  1 has          1 grids (       0,       1,       0,)
 Level  2 has          8 grids (       4,       4,       4,)
 Level  3 has         64 grids (      32,      32,      32,)
 Level  4 has        512 grids (     256,     256,     256,)
 Level  5 has       4096 grids (    2048,    2048,    2048,)
 Level  6 has      32768 grids (   16384,   16384,   16384,)
 Level  7 has     262144 grids (  131072,  131072,  131072,)
 Main step=      1 mcons= 0.00E+00 econs= 0.00E+00 epot=      NaN ekin= 0.00E+00
 Fine step=      1 t= 2.71350E+04 dt= 2.714E+04 a= 1.000E+00 mem=17.3%  0.0%
 Run completed
 Total elapsed time:   4.4218359169999957     
 --------------------------------------------------------------------

     minimum       average       maximum  standard dev        std/av       %   rmn   rmx  TIMER
       0.023         0.023         0.023         0.000         0.006     0.2     1   2    coarse levels           
       0.055         0.055         0.055         0.000         0.000     0.5     2   1    refine                  
       1.397         1.397         1.397         0.000         0.000    13.9     1   2    load balance            
       0.506         0.509         0.513         0.003         0.007     5.1     2   1    io                      
       7.884         7.884         7.884         0.000         0.000    78.6     1   2    poisson                 
       0.009         0.012         0.016         0.003         0.282     0.1     1   2    rho                     
       0.148         0.148         0.148         0.000         0.000     1.5     1   2    flag                    
      10.034     100.0    TOTAL
Note: The following floating-point exceptions are signalling: IEEE_INVALID_FLAG
Note: The following floating-point exceptions are signalling: IEEE_INVALID_FLAG IEEE_DENORMAL
</code></pre>
<p>The namelist file I am running is</p>
<pre><code>#!fortran
&amp;RUN_PARAMS
pic=.true.
poisson=.true.
nrestart=0
nremap=10
nsubcycle=1,2,
ncontrol=1
/

&amp;INIT_PARAMS
filetype='dice'
initfile(1)='/uufs/astro.utah.edu/common/home/u1281896/NBodies/DICE_IC_FILES'
/

&amp;DICE_PARAMS
ic_file='dice_spiral.g2'
ic_nfile=1
ic_ifout=1
ic_format='Gadget2'
ic_center=0.0,0.0,0.0
ic_scale_pos=1.0
ic_scale_vel=1.0
ic_scale_mass=1.0
ic_scale_u=1.0
ic_scale_age=1.0
ic_scale_metal=1.0
ic_head_name='HEAD'
ic_pos_name='POS '
ic_vel_name='VEL '
ic_mass_name='MASS'
ic_id_name='ID  '
ic_u_name='U   '
ic_metal_name='Z   '
ic_age_name='AGE '
IG_rho=1.0D-6
IG_T2=1.0D6
IG_metal=1.0D-4
amr_struct=.false.
gadget_scale_l=3.085677581282D21
gadget_scale_v=1.0D5
gadget_scale_m=1.9891D43
gadget_scale_t=3.15360e+13
ic_skip_type=-1
cosmo_add_gas_index=-1
ic_mag_const=0.0,0.0,0.0
ic_mag_center_x=0.0
ic_mag_center_y=0.0
ic_mag_center_z=0.0
ic_mag_axis_x=0.0
ic_mag_axis_y=0.0
ic_mag_axis_z=1.0
ic_mag_scale_R=1.0
ic_mag_scale_H=1.0
ic_mag_scale_B=0.0
/
&amp;REFINE_PARAMS
m_refine=7*8.,
/
&amp;BOUNDARY_PARAMS
nboundary=6
bound_type=2,2,2,2,2,2
ibound_min=-1,1,-1,-1,-1,-1
ibound_max=-1,1,1,1,1,1
jbound_min=0,0,-1,1,-1,-1
jbound_max=0,0,-1,1,1,1
kbound_min=0,0,0,0,-1,1
kbound_max=0,0,0,0,-1,1
no_inflow=.true.
/

&amp;OUTPUT_PARAMS
noutput=5
tout=0.0,20.0,40.0,60.0,80.0
tend=80.0
/

&amp;AMR_PARAMS
levelmin=7
levelmax=14
ngridtot=2000000
nparttot=3000000
nexpand=1
boxlen=1.0
/


&amp;HYDRO_PARAMS
gamma=1.6666667
courant_factor=0.8
slope_type=1
pressure_fix=.true.
scheme='muscl'
/

&amp;POISSON_PARAMS
epsilon=1.d-2
/
</code></pre>
<p>Is anyone familiar enough with the codes to help? I reached out to the author of RAMSES, but he seems to be MIA!</p>

<galaxy><gravity><cosmology><n-body-simulations>
RAMSES fine multigrid Poisson solver fails to converge?
BooleanDesigns
# RAMSES fine multigrid Poisson solver fails to converge?

(Asked by: username_0 on 2022-09-04)

I am working on setting up N-body simulations of galaxy mergers. The initial conditions are generated from the DICE code, and looking at them, they seem very realistic. Unfortunately, when I let RAMSES run, it fails to converge. The output looks something like this

```
Initial mesh structure
 Level  1 has          1 grids (       0,       1,       0,)
 Level  2 has          8 grids (       4,       4,       4,)
 Level  3 has         64 grids (      32,      32,      32,)
 Level  4 has        512 grids (     256,     256,     256,)
 Level  5 has       4096 grids (    2048,    2048,    2048,)
 Level  6 has      32768 grids (   16384,   16384,   16384,)
 Level  7 has     262144 grids (  131072,  131072,  131072,)
 Starting time integration
 Load balancing AMR grid...
   ==> Level=    7 Step=   10 Error=       NaN
 WARN: Fine multigrid Poisson failed to converge...
 Fine step=      0 t= 0.00000E+00 dt= 2.714E+04 a= 1.000E+00 mem=17.3%  0.0%
 Time elapsed since last coarse step:    5.76 s        5.50 mus/pt        5.50 mus/pt (av)
 Used memory:    799.9 MB
 Total running time:   97.1599960     s
   ==> Level=    7 Step=   10 Error=       NaN
 WARN: Fine multigrid Poisson failed to converge...
 Mesh structure
 Level  1 has          1 grids (       0,       1,       0,)
 Level  2 has          8 grids (       4,       4,       4,)
 Level  3 has         64 grids (      32,      32,      32,)
 Level  4 has        512 grids (     256,     256,     256,)
 Level  5 has       4096 grids (    2048,    2048,    2048,)
 Level  6 has      32768 grids (   16384,   16384,   16384,)
 Level  7 has     262144 grids (  131072,  131072,  131072,)
 Main step=      1 mcons= 0.00E+00 econs= 0.00E+00 epot=      NaN ekin= 0.00E+00
 Fine step=      1 t= 2.71350E+04 dt= 2.714E+04 a= 1.000E+00 mem=17.3%  0.0%
 Run completed
 Total elapsed time:   4.4218359169999957     
 --------------------------------------------------------------------

     minimum       average       maximum  standard dev        std/av       %   rmn   rmx  TIMER
       0.023         0.023         0.023         0.000         0.006     0.2     1   2    coarse levels           
       0.055         0.055         0.055         0.000         0.000     0.5     2   1    refine                  
       1.397         1.397         1.397         0.000         0.000    13.9     1   2    load balance            
       0.506         0.509         0.513         0.003         0.007     5.1     2   1    io                      
       7.884         7.884         7.884         0.000         0.000    78.6     1   2    poisson                 
       0.009         0.012         0.016         0.003         0.282     0.1     1   2    rho                     
       0.148         0.148         0.148         0.000         0.000     1.5     1   2    flag                    
      10.034     100.0    TOTAL
Note: The following floating-point exceptions are signalling: IEEE_INVALID_FLAG
Note: The following floating-point exceptions are signalling: IEEE_INVALID_FLAG IEEE_DENORMAL

```

The namelist file I am running is

```
#!fortran
&RUN_PARAMS
pic=.true.
poisson=.true.
nrestart=0
nremap=10
nsubcycle=1,2,
ncontrol=1
/

&INIT_PARAMS
filetype='dice'
initfile(1)='/uufs/astro.utah.edu/common/home/u1281896/NBodies/DICE_IC_FILES'
/

&DICE_PARAMS
ic_file='dice_spiral.g2'
ic_nfile=1
ic_ifout=1
ic_format='Gadget2'
ic_center=0.0,0.0,0.0
ic_scale_pos=1.0
ic_scale_vel=1.0
ic_scale_mass=1.0
ic_scale_u=1.0
ic_scale_age=1.0
ic_scale_metal=1.0
ic_head_name='HEAD'
ic_pos_name='POS '
ic_vel_name='VEL '
ic_mass_name='MASS'
ic_id_name='ID  '
ic_u_name='U   '
ic_metal_name='Z   '
ic_age_name='AGE '
IG_rho=1.0D-6
IG_T2=1.0D6
IG_metal=1.0D-4
amr_struct=.false.
gadget_scale_l=3.085677581282D21
gadget_scale_v=1.0D5
gadget_scale_m=1.9891D43
gadget_scale_t=3.15360e+13
ic_skip_type=-1
cosmo_add_gas_index=-1
ic_mag_const=0.0,0.0,0.0
ic_mag_center_x=0.0
ic_mag_center_y=0.0
ic_mag_center_z=0.0
ic_mag_axis_x=0.0
ic_mag_axis_y=0.0
ic_mag_axis_z=1.0
ic_mag_scale_R=1.0
ic_mag_scale_H=1.0
ic_mag_scale_B=0.0
/
&REFINE_PARAMS
m_refine=7*8.,
/
&BOUNDARY_PARAMS
nboundary=6
bound_type=2,2,2,2,2,2
ibound_min=-1,1,-1,-1,-1,-1
ibound_max=-1,1,1,1,1,1
jbound_min=0,0,-1,1,-1,-1
jbound_max=0,0,-1,1,1,1
kbound_min=0,0,0,0,-1,1
kbound_max=0,0,0,0,-1,1
no_inflow=.true.
/

&OUTPUT_PARAMS
noutput=5
tout=0.0,20.0,40.0,60.0,80.0
tend=80.0
/

&AMR_PARAMS
levelmin=7
levelmax=14
ngridtot=2000000
nparttot=3000000
nexpand=1
boxlen=1.0
/

&HYDRO_PARAMS
gamma=1.6666667
courant_factor=0.8
slope_type=1
pressure_fix=.true.
scheme='muscl'
/

&POISSON_PARAMS
epsilon=1.d-2
/

```

Is anyone familiar enough with the codes to help? I reached out to the author of RAMSES, but he seems to be MIA!

**Tags:** galaxy, gravity, cosmology, n-body-simulations


---

## 1 answers

### Answer by username_0 on 2023-01-23. Score: 1 | Accepted answer

This can be dealt with by enabling the `hydro` parameter in the `RUN_PARAMS` section of the namelist file.


---

