Each ‘‘galaxy’’ can have different combinations of density profiles, velocity distributions and spatial shapes, the center of mass and velocity can be specified individually for each one.
PARAMETER (Npmx = 50000) !Maximum number of particles PARAMETER (Ngmx = 50) !Maximum number of galaxies INTEGER iseed !random number generator seed CHARACTER*72 comment !general commentary for init. cond. INTEGER Np !# of points in simulation INTEGER Ngals !# of galaxies INTEGER nframe !# of frame REAL time !time for frame CHARACTER*72 cparam(Ngmx) !galaxies’ character string array LOGICAL lparam(16,Ngmx) !galaxies’ logical parameters array INTEGER iparam(12,Ngmx) !galaxies’ integer parameters array REAL rparam(40,Ngmx) !galaxies’ real parameters array INTEGER index(Npmx) !array used to indicate unbound particles REAL lum(Npmx), m(Npmx), x(3,Npmx), v(3,Npmx) !part. lum, mass, pos. & vel. COMMON /snapshot/ iseed,comment,Np,Ngals,nframe,time, * cparam,lparam,iparam,rparam,index,m,lum,x,vThe following snippet of code would have written the unformatted version of this SNAP data:
open(99, file = snapfile // ’SNAP_u.dat ’, form=’unformatted’,status=’new’)
write(99) iseed,comment,Np,Ngals,nframe,time,
(cparam(i),i=1,Ngals),
((lparam(i,j),i=1,16),j=1,Ngals),
((iparam(i,j),i=1,12),j=1,Ngals),
((rparam(i,j),i=1,40),j=1,Ngals),
(index(i),i=1,Np),(m(i),i=1,Np),
(lum(i),i=1,Np),
((x(i,j),i=1,3),j=1,Np),((v(i,j),i=1,3),j=1,Np)
Reading this format is exactly the same. Note the convention that the filename
has a fixed extension SNAP_u.dat for unformatted format, and the extension
SNAP_f.dat for the formatted version. To convert between these two, see snapformat(1LAAC)
.
The size of this data is 92 + 344*Ngals + 36*Np, assuming 4 bytes per REAL and INTEGER.
PARAMETERS:
Npmx: Maximum number of particles Ngmx: Maximum number of galaxies
CHARACTER VARIABLES:
comment: Commentary
INTEGER VARIABLES:
iseed: seed for random number generator Np: Number of points in initial conditions ngals: Number of galaxies nframe: Frame number in a series of snapshots (1=first) time: Time of the snapshot index(Npmx): If (0), bound particle; if (1), unbound.
REAL VARIABLES:
m(Npmx): masses of individual particles lum(Npmx): light to mass ratio for each particle x(3,Npmx): spatial cartesian coordinates of particles v(3,Npmx): cartesian velocity components of particles
CHARACTER VARIABLES:
cparam*72(Ngmx) Comment
LOGICAL VARIABLES:
lparam(16,Ngmx) i=1: Equal masses for particles? 2: Non-spherical shape? 3: Rotation measured? 4: Softened velocities? 5: Principal axes aligned with frame of reference? 6: Unbound particles marked? 7: Density profile fitted? 8-16: Not used
INTEGER VARIABLES:
iparam(12,Ngmx) i=1: Number of points 2: Density profile code: 1) constant density 2) power-law 3) isochrone 4) Plummer 5) Rood (modified Hubble) 6) King 7) de-Vaucouleurs 8) Jaffe 9) Hernquist 3: Velocity distribution: 1) isotropic 2) anisotropic (Opsikov-Merritt) 3) Circular orbits 4: Mass function: 1) equal masses 2) power-law 5: Number of bound particles 6-12: Not used
REAL VARIABLES:
rparam(40,Ngmx): i=1: pwr-law index, concentr., or 1D central vel. disp. 2: rt (total radius) 3: rh (half mass radius) 4: Mg (Mass of galaxy) 5: Ug (Potential energy of galaxy) 6: ro (core radius) 7: dens_o (central density) 8: ra (anisotropy radius) 9: (2T/U)tot (total virial ratio) 10: (2T/U)rot (virial ratio for rotation) 11: (X/Z) (major to minor axis ratio at 80% mass fract.) 12: (Y/Z) (interm. to minor axis ratio at 80% ...... ) 13-15: (xo,yo,zo) (coordinates of center of galaxy) 16-18: (vxo,vyo,vzo) (vel. comp. of center of galaxy) 19: m1/<mi> (mass ratio of 1st part. to mean of others) 20: Mass function index 21: m_max/m_min (mass dynamical range) 22: e1i^2 (squared soft. length for 1-i interaction) 23: eij^2 (squared soft. length for i-j interaction) 24: T (Kinetic energy of galaxy) 25: E (Total energy of galaxy) 26: vrms (rms velocity of galaxy) 27: Tb (Kinetic energy of bound galaxy) 28: Ub (potential energy of bound galaxy) 29: Eb (total energy of bound galaxy) 30: Mbnd (mass of bound galaxy) 31: Tcm (kinetic energy of center of mass motion) 32: DE/E (fractional change in total energy) 33: DM/M (fractional change in mass) 34-40: Not used
Machine dependant FORTRAN binary format.
usr/aguilar/galmaker examples snap.inc The COMMON/SNAP/ definition
CHARACTER*72 comment !general commentary for init. cond. INTEGER Np !# of points in simulation REAL time !time for frame INTEGER nframe !# of frame REAL soften, m1, m2, mi, e12, e1i, eij, Vrms, Tcross, u, k, e REAL x(3,*),v(3,*) !part. lum, mass, pos. & vel. COMMON /SNAPSHOT/ iseed,comment,Np,Ngals,nframe,time, * cparam,lparam,iparam,rparam,index,m,lum,x,vThe following snippet of code would have written the unformatted version of this SNAP data:
open(99, file = snapfile // ’SNAP_u.dat ’, form=’unformatted’,status=’new’)
write(99) iseed,comment,Np,Ngals,nframe,time,
(cparam(i),i=1,Ngals),
((lparam(i,j),i=1,16),j=1,Ngals),
((iparam(i,j),i=1,12),j=1,Ngals),
((rparam(i,j),i=1,40),j=1,Ngals),
(index(i),i=1,Np),(m(i),i=1,Np),
(lum(i),i=1,Np),
((x(i,j),i=1,3),j=1,Np),((v(i,j),i=1,3),j=1,Np)
Reading this format is exactly the same. Note that the filename has a fixed
extension SNAP_u.dat for unformatted format, and an extension SNAP_f.dat
for the formatted version. To convert between these two, see snapformat(1LAAC)
.
2/10/92 Created Luis A. Aguilar 21-nov-93 man5 created PJT 14-jun-94 documented v1 and v2 PJT