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It is important to check the return value in IRET to ensure the call has been successful.
Calls to INTIN are not required before calling INTUVP because the input GRIB products provide sufficient descriptive information. However, before calling INTUVU, it necessary to call INTIN to describe the input truncation.
If INTOUT is called before INTUVP or INTUVU, the U and V fields will be generated and also interpolated during production. Otherwise, the U and V fields will have the same form as the vorticity and divergence fields; eg spectral vorticity and divergence fields generate spectral U and V.
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The returned value is 0 if the call is successful.