Dimensions

The number of cells in the x, y, & z direction for the core region of each Info structure is stored in the array

Info%mX(1:3)

and often one will declare local variables mx, my, & mz to avoid repeatedly having to type Info%mx(d).

mx=Info%mX(1)
my=Info%mX(2)
mz=Info%mX(3)

The data within this core region (which does not include ghost zones) is stored in Info%q(1:mx,1:my,1:mz,1:NrHydroVars) where NrHydroVars represents the number of fluid variables including tracers. If running with fewer than 3 dimensions, the unused dimensions have an extent of 1.

Before we can initialize a cell we must calculate it's physical location and extent. To do so we need to know the cell size for the Info's AMR level. The properties of each level are stored in the levels(:) array. To access this data we must use the GlobalDeclarations module by adding the following to our module at the top.

USE GlobalDeclarations

Then to access properties of level n - for example the current time that level has advanced to we would use levels(n)%tnow. If we wanted to now the current time step for level n we could use levels(n)%dt. And to access the cell size for level n we could use levels(n)%dx. Since the level a given info structure resides on is stored in Info%level, the cell size is given by levels(Info%level)%dx. So to get the x-position of the center of a cell with x-index i we could use

xlower=Info%xBounds(1,1)
dx=levels(Info%level)%dx
x=xlower+(REAL(i)-.5)*dx

Note we subtract 0.5 from the index before multiplying by the spacing since we are calculating the cell center. And that the cell actually goes from x-.5*dx to x+.5*dx. Also note that we convert the integer to a real before subtracting .5. And if we want to calculate x,y,z we could use

xlower=Info%xBounds(1,1)
dx=levels(Info%level)%dx
x=xlower + (REAL(i)-.5)*dx
y=ylower + (REAL(j)-.5) * dx
z=zlower + (REAL(k)-.5) * dx
IF (nDim < 2) y=ylower
IF (nDim < 3) z=zlower

The last two lines are necessary since we don't want to add .5 to the y or z dimensions if we are only in 1D or 2D. We could also streamline this using the Fortran MERGE function and storing (/x,y,z/) in an array pos(:) using

pos=Info%xBounds(:,1)+merge((REAL((/i,j,k/))-.5)*dx, (/0d0,0d0,0d0/), nDim < (/1,2,3/))

Finally since the precision of the various info fields related to spatial position is a parameter xPrec (could be single or double), some compilers will complain unless you convert (/i,j,k/ as well as .5 to the right kind of REAL.

pos=Info%xBounds(:,1)+merge((REAL((/i,j,k/),KIND=xPREC)-half)*dx, (/0d0,0d0,0d0/), nDim < (/1,2,3/))

Note that the variable half is a parameter equal to REAL(.5, KIND=xPREC) declared in GlobalDeclarations

Finally there is a function already called CellPos that does the same calculation which makes life much easier.

 pos=CellPos(Info, i, j, k)

The Info%aux array is a little different. The aux array holds magnetic flux values, which are face-averaged. This means that every volume averaged value in Info%q is bracketed in each dimension by two Info%aux values. To accommodate the extra values, Info%aux is a 1:mx+1 by 1:my+1 by 1:mz+1 box, but the aux dimensions are actually different for each variable:

Bx = Info%aux(1:mx+1, 1:my, 1:mz, 1)
By = Info%aux(1:mx, 1:my+1, 1:mz, 2)
Bz = Info%aux(1:mx, 1:my, 1:mz+1, 3)

The additional cells (the ones in the "upper-front right" corner of the aux array) are not used. To locate the center of the face for the Bx fields, we would subtract half*dx from the cell center.

x_pos=CellPos(Info, i, j, k)-(/half,0d0,0d0/)

and for By and Bz we could use

y_pos=CellPos(Info, i, j, k)-(/0d0,half,0d0/)
z_pos=CellPos(Info, i, j, k)-(/0d0,0d0,half/)