◆ Costmb()

One-dimensional cosine backward transform (multiple sequences)

Purpose: This routine computes the one-dimensional Fourier transform of multiple even sequences within a real array. This is referred to as the backward transform or Fourier synthesis, transforming the sequence from spectral to physical space.
R(l*jump+j) = ΣR(l*jump+k)cos(πjk/(N-1)) (Σ for k = 0 to N-1) (l = 0 to lot-1, j = 0 to N-1)

This transform is normalized since a call to Costmb followed by a call to Costmf (or vice-versa) reproduces the original array subject to algorithmic constraints, roundoff error, etc.

Parameters

[in]	Lot	Number of sequences to be transformed. (Lot >= 1)
[in]	Jump	Increment between the locations, in array R(), of the first elements of two consecutive sequences to be transformed. (Jump >= 1)
[in]	N	Length of the sequence to be transformed. (N >= 1) (The transform is most efficient when N-1 is a product of small primes)
[in,out]	R()	Array R(LR - 1) (LR >= (Lot - 1)Jump + Inc(N - 1) + 1) [in] The sequences to be transformed. [out] The Fourier backward transformed sequences of data.
[in]	Wsave()	Array Wsave(LWsave - 1) (LWsave >= 2*N + ln(N)/ln(2) + 4) Work data. Its contents must be initialized with a call to Costmi before the first call to Costmf or Costmb for a given transform length N.
[out]	Info	= 0: Successful exit. = -1: The argument Lot had an illegal value. (Lot < 1, or, Lot, Jump, N and Inc are inconsistent) = -2: The argument Jump had an illegal value. (Jump < 1) = -3: The argument N had an illegal value. (N < 1) = -4: The argument R() had an illegal value. (Array R() is not big enough) = -5: The argument Wsave() had an illegal value. (Array Wsave() is not big enough) = -7: The argument Inc had an illegal value. (Inc < 1)
[in]	Inc	(Optional) Integer increment between the locations, in array R(), of two consecutive elements within the sequence. (Inc >= 1) (default = 1)