Encyclopaedia Index

### (e) The indicial expressions

The indicial expressions referred to above are linear functions of the cell-location-coordinate indices, IX, IY and IZ; and the coefficients in the linear functions involve the total numbers of cells in these three coordinate directions, namely NX, NY and NZ.

The indicial expressions are:

• for XWV's, IX
• for YWV's, IY
• for ZWV's, IZ
• for SWV's and for FFV's other than WSV's, IY+NY*(IX-1)
• for WSV's, IY+NY*(IX-1)+NX*NY*(IZ-1)
• for PWV's, (IY-IYF+1)+(IYL-IYF+1)*(IX-IXF)+(IYL-IYF+1)* (IXL-IXF+1)*(IZ-IZF)

These formulae express the fact that, on a slab of fixed IZ, the cells are ordered as indicated below:

IY increasing

```
^
|    NY      2*NY    3*NY    .........   (NX-1)*NY    NX*NY
|    NY-1    2*NY-1                                   NX*NY-1
|    NY-2    .                                           .
|    .       .                                           .
|    .       .                                           .
|    .       .                                           .
|    4       .                                           .
|    3       NY+3                                        .
|    2       NY+2                                        .
|    1       NY+1    2*NY+1  ......................   (NX-1)*NY+1
|
-------------------------------------------------> IX increasing
```
wbs