PK_ERROR_code_t PK_ATTRIB_ask_doubles
(
--- received arguments ---
PK_ATTRIB_t     attrib,             --- attribute
int             field_no,           --- field number (>= 0)

--- returned arguments ---
int      *const n_doubles,          --- number of doubles (>=0)
double  **const doubles             --- doubles (optional)
)


This function returns the array of doubles from field field_no
of the given attribute.


Specific Errors:
    PK_ERROR_bad_field_number       The attribute does not have a field with
                                    this number
    PK_ERROR_field_of_wrong_type    The field is not a double field


The output array doubles is optional.  If it is set to NULL, the function
will only return the number of doubles in the field.