twist

DESCRIPTION

"twist" is a subroutine that may be used to optimize the compression carried out by squeeze, by use of any combination (or all) of the implemented compression algorithms. However, "twist" works slower than "squeeze", and requires about 33% more memory. See squeeze sample for a "walk-thru" of how "squeeze" works.

SYNTAX

subroutine

twist

( nalgorithms,algorithms,ldat,leading,trailing,length, idata,printlevel,algorithm,maxsize,iwork,error )

INPUT, OUTPUT VARIABLES

Input:

nalgorithms	(i)	-	dimension of 'algorithms()', i.e., no. of compression algorithms to attempt
algorithms	(I)	-	list of compression algorithma to attempt values: 1 (2-1), 2 (3-1), 3 (4-1), 4 (3-2), 5 (5-1), 6 (4-2) etc. presently implemented: 1, 4, 6, 9 if algorithms(1) = 0: signal that all implemented compression algorithms will be attempted
ldat	(i)	-	no. of values to consider in 'idata()' vector (including leading & trailing) will be reset if compression is successful (see information on output variables below)
leading	(i)	-	no. of leading entries in 'idata()' that should not be compressed
trailing	(i)	-	no. of trailing entries in 'idata()' that should not be compressed
length	(i)	-	dimension of 'idata()' (suggested value: leading+nx*ny+trailing); left unchanged by "twist"
idata	(I2)	-	leading entries, field, trailing entries
printlevel	(i)	-	indicates amount of information written to the default output device: <=0 : no information 1 : best algorithm >=2 : as 1, and intermediate results from all attempts
maxsize	(i)	-	dimension of 'iwork'; minimum value: nx*ny+trailing

Output:

algorithm	(i)	-	compression algorithm used [best compression of the algorithms listed on input]
ldat	(i)	-	length of the compressed 'idata()' vector
idata	(I2)	-	leading entries, compressed field, trailing entries
error	(i)	-	in "twist", set to: 0 if no error is detected 1 if non-implemented 'algorithm' is selected in "squeeze", set to: 1 if non-implemented 'algorithm' is selected 2 if dimension of 'factors()' is too small 3 if # leading + # trailing > input 'ldat'

Work:

iwork

(I2)

-

work space vector, temporary storage in "squeeze"

DEPENDENCIES

Subroutine: squeeze, speedsqueeze