| 57 | | ==== Dimensions ==== |
| 58 | | The number of cells in the x, y, & z direction for the '''core''' region of each Info structure is stored in the array |
| 59 | | {{{ |
| 60 | | Info%mX(1:3) |
| 61 | | }}} |
| 62 | | and often one will declare local variables {{{mx, my, & mz}}} to avoid repeatedly having to type Info%mx(d). |
| 63 | | {{{ |
| 64 | | mx=Info%mX(1) |
| 65 | | my=Info%mX(2) |
| 66 | | mz=Info%mX(3) |
| 67 | | }}} |
| 68 | | |
| 69 | | 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. |
| 70 | | |
| 71 | | 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. |
| 72 | | {{{ |
| 73 | | USE GlobalDeclarations |
| 74 | | }}} |
| 75 | | 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 |
| 76 | | {{{ |
| 77 | | xlower=Info%xBounds(1,1) |
| 78 | | dx=levels(Info%level)%dx |
| 79 | | x=xlower+(REAL(i)-.5)*dx |
| 80 | | }}} |
| 81 | | 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 |
| 82 | | {{{ |
| 83 | | xlower=Info%xBounds(1,1) |
| 84 | | dx=levels(Info%level)%dx |
| 85 | | x=xlower + (REAL(i)-.5)*dx |
| 86 | | y=ylower + (REAL(j)-.5) * dx |
| 87 | | z=zlower + (REAL(k)-.5) * dx |
| 88 | | IF (nDim < 2) y=ylower |
| 89 | | IF (nDim < 3) z=zlower |
| 90 | | }}} |
| 91 | | 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 |
| 92 | | {{{ |
| 93 | | pos=Info%xBounds(:,1)+merge((REAL((/i,j,k/))-.5)*dx, (/0d0,0d0,0d0/), nDim < (/1,2,3/)) |
| 94 | | }}} |
| 95 | | 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. |
| 96 | | {{{ |
| 97 | | pos=Info%xBounds(:,1)+merge((REAL((/i,j,k/),KIND=xPREC)-half)*dx, (/0d0,0d0,0d0/), nDim < (/1,2,3/)) |
| 98 | | }}} |
| 99 | | Note that the variable {{{half}}} is a parameter equal to {{{REAL(.5, KIND=xPREC)}}} declared in GlobalDeclarations |
| 100 | | |
| 101 | | Finally there is a function already called !CellPos that does the same calculation which makes life much easier. |
| 102 | | {{{ |
| 103 | | pos=CellPos(Info, i, j, k) |
| 104 | | }}} |
| 105 | | |
| 106 | | |
| 107 | | [[BR]] |
| 108 | | 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: |
| 109 | | |
| 110 | | {{{ |
| 111 | | Bx = Info%aux(1:mx+1, 1:my, 1:mz, 1) |
| 112 | | By = Info%aux(1:mx, 1:my+1, 1:mz, 2) |
| 113 | | Bz = Info%aux(1:mx, 1:my, 1:mz+1, 3) |
| 114 | | }}} |
| 115 | | |
| 116 | | 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. |
| 117 | | {{{ |
| 118 | | x_pos=CellPos(Info, i, j, k)-(/half,0d0,0d0/) |
| 119 | | }}} |
| 120 | | and for By and Bz we could use |
| 121 | | {{{ |
| 122 | | y_pos=CellPos(Info, i, j, k)-(/0d0,half,0d0/) |
| 123 | | z_pos=CellPos(Info, i, j, k)-(/0d0,0d0,half/) |
| 124 | | }}} |
| 125 | | [[BR]] |
