Fortran-77 syntax is used for specifying the expression, which may contain the usual intrinsic functions, plus a few extra ones. An appendix in SUN/61 gives a full description of the syntax used and an up to date list of the functions available. The expression may be up to 132 characters long and is case insensitive.
These parameters are particularly useful for supplying the values of constants when writing procedures, where the constant may be determined by a command-language variable, or when the constant is stored in a data structure such as a global parameter. In other cases, constants should normally be given literally as part of the expression, as in "IZ 2.77".
The set of 7 tokens named CA, CB, ...CG is used to obtain the data co-ordinates from the primary input NDF data structure. Any of the 7 parameters may appear in the expression. The order defines which axis is which, so for example, "2 CF CB CB" means the first-axis data co-ordinates squared, plus twice the co-ordinates along the second axis. There must be at least one input NDF in the expression to use the CA-CG tokens, and it must have dimensionality of at least the number of CA-CG tokens given.
The set of 7 tokens named XA, XB, ...XG is used to obtain the pixel co-ordinates from the primary input NDF data structure. Any of the 7 parameters may appear in the expression. The order defines which axis is which, so for example, "SQRT(XE) XC" means the first-axis pixel co-ordinates plus the square root of the co-ordinates along the second axis. Here no input NDF need be supplied. In this case the dimensionality of the output NDF is equal to the number of XA-XG tokens in the expression. However, if there is at least one NDF in the expression, there should not be more XA-XG tokens than the dimensionality of the output NDF (given as the intersection of the bounds of the input NDFs).
The main value of the variance-estimation algorithm used here arises when the expression to be evaluated is too complicated, or too infrequently used, to justify the work of deriving a direct formula for the variance. It is also of value when the data errors are especially large, so that the linear approximation normally used in error analysis breaks down.
There is no variance processing when there are no tokens for input NDF structures.
If output variance values are being calculated and the QUICK parameter is set to TRUE, then the execution time will be multiplied by an approximate factor ( 1), where n is the number of input NDFs which contain a VARIANCE component. If QUICK is set to FALSE, then the execution time will be multiplied by an approximate factor ( 1).
KAPPA --- Kernel Application Package