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Formulas can be extended up to 128 characters. When designing complex equations, it is often helpful to develop the equation in pieces, or terms. In these cases, GDDIAG can be used to calculate store the terms, for ultimate use in the final expansion.
When storing grids with GDDIAG, the variable GRDNAM will be used to define a name for the new parameter. If this parameter is left blank, GEMPAK will compose a name based on the variables and functions used in the expression.
Many times, a single GLEVEL, GDATTIM, or even GVCORD is not sufficient for calculating all the quantities in a formula. In these cases we need to use in-line modifiers.
In line expansions allow us to modify the values used for a parameter in a per-variable manner.
The following may be used to specify a value other than that which a variable would obtain if using the values specified in the user interface variables:
Additionally, we may need to specify more than 1 value, as in the case of a layer quantity such as thickness between pressure levels, or as in time differences such as the height change of a surface with time.
When we have to specify more than 1 value for a level or time parameter (either in GLEVEL and GDATTIM, or through the in-line modifiers) the values are separated with a : (colon).
When multiple grid files are used, a + character is used in the GDFILE variable to separate the filenames. Then when referencing which file a grid field should be found, the variable is appended with +n, where n is the number of the grid file in the order given in GDFILE.
Well thats quite a list of new concepts. Must be time for some
Exercises!!
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