## pdefwrite

When GrADS opens a descriptor with a `PDEF` entry that contains options such as `lcc`, `lccr`, `nps`, `sps`, et. al, it calculates the interpolation weights internally and stores them in memory for later use. These calculations can take some time for high resolution grids. There is a significant performance advantage gained from reading in the interpolation weights from an external file instead of calculating them every time you open the descriptor. Introduced in GrADS version 2.1.0, the `pdefwrite` command will write out the interpolation weights that have been calculated internally for these special types of `PDEF` entries. The file it creates can be used with a ‘`PDEF bilin`’ entry instead.

### Syntax

`pdefwrite filename`

where:

`filename` The name of the output file. If this file exists, it will be replaced.
``

### Usage Notes

1. `pdefwrite` works with GrADS version 2.1.0+.
2. The `pdefwrite` command will return an error message if you use it with a default file that does not use `PDEF` or already has an external `PDEF` file. If there are no errors, `pdefwrite` will return a complete `PDEF` entry that points to the file it just created.

### Example

1. Suppose you have a descriptor that contains the following three entries:
   `pdef 4736 3000 lcc 23.00 -120 1 1 40.0 40.0 -100 1016.2360 1016.150
   xdef 6650 linear -130.0 0.01
   ydef 3500 linear 20.0 0.01`
2. Open this descriptor, then invoke pdefwrite with a file name as an argument.
   `ga-> pdefwrite myfile.pdef
   `
3. GrADS will return the syntax for the new `PDEF` entry:
   `pdef 4736 3000 bilin stream binary-little ^myfile.pdef`
4. Rewrite your descriptor to use this new `PDEF` entry instead. Don’t change the `XDEF` and `YDEF` statements — those match the `PDEF` file you created.
5. Keep the `PDEF` file (`myflile.pdef`) and the descriptor file together in the same directory -- this is important because of the ^ before the `PDEF` file's name in the `PDEF` entry. If you want to put the descriptor and `PDEF` files in separate locations, change the ^ in the entry to the `PDEF` file's full path, like this:
   `pdef 4736 3000 bilin stream binary-little /your/path/to/myfile.pdef`