◆ cfft2i()

Initialization of work data for cfft2f and cfft2b

Purpose: cfft2i initializes array wsave[] for use in its companion routines cfft2f and cfft2b. The prime factorization of n together with a tabulation of the trigonometric functions are computed and stored in array wsave[].

Note - The initialization of wsave[] is not necessary for the succeeding call of cfft2f or cfft2b for the same l and m values. If the value of l or m has been changed, wsave[] should be re-initialized by this routine.

Parameters

[in]	l	The number of elements to be transformed in the first dimension of the two-dimensional complex array c[][]. (l >= 1) The transform is most efficient when l is a product of small primes.
[in]	m	The number of elements to be transformed in the second dimension of the two-dimensional complex array c[][]. (m >= 1) The transform is most efficient when m is a product of small primes.
[out]	wsave[]	Array wsave[lwsave] Work data, containing the prime factors of n and also containing certain trigonometric values which will be used in routines cfft2f and cfft2b.
[in]	lwsave	The length of the array wsave[]. (lwsave >= 2*(l + m) + ln(l)/ln(2) + ln(m)/ln(2) + 8)
[out]	info	= 0: Successful exit = -1: The argument l had an illegal value (l < 1) = -2: The argument m had an illegal value (m < 1) = -4: The argument lwsave had an illegal value (lwsave not big enough)