|IDL Reference Guide: Procedures and Functions|
The DOUBLE function converts Expression into a double-precision floating-point value.
Result = DOUBLE(Expression[, Offset [, D1 [, ..., D8]]])
Returns a double-precision floating-point value or array of the same dimensions as the result of the Expression. If Expression is a complex number, DOUBLE returns the real part.
The expression to be converted to double-precision, floating-point.
Offset from beginning of the Expression data area. Specifying this argument allows fields of data extracted from Expression to be treated as double-precision, floating-point data. See the description in Working with Data in IDL for details.
When extracting fields of data, the Di arguments specify the dimensions of the result. If no dimension arguments are given, the result is taken to be scalar.
The Di arguments can be either an array or a series of scalar expressions specifying the dimensions of the result. If a single argument is specified, it can be either a scalar expression or an array of up to eight elements. If multiple arguments are specified, they must all be scalar expressions. Up to eight dimensions can be specified.
When converting from a string argument, it is possible that the string does not contain a valid floating-point value and no conversion is possible. The default action in such cases is to print a warning message and return 0. The ON_IOERROR procedure can be used to establish a statement to be jumped to in case of such errors.
This routine is written to make use of IDL's thread pool, which can increase execution speed on systems with multiple CPUs. The values stored in the !CPU system variable control whether IDL uses the thread pool for a given computation. In addition, you can use the thread pool keywords TPOOL_MAX_ELTS, TPOOL_MIN_ELTS, and TPOOL_NOTHREAD to override the defaults established by !CPU for a single invocation of this routine. See Thread Pool Keywords for details.
Suppose that A contains the integer value 45. A double-precision, floating-point version of A can be stored in B by entering:
B = DOUBLE(A) PRINT, B