/**
 * Real FFT: compute the full FFT of a real signal and keep only the first
 * `floor(n/2)+1` bins — the non-redundant half of the conjugate-symmetric spectrum.
 *
 * @param x Real input signal
 * @returns `{ re, im }` arrays of length `floor(n/2)+1`
 */
export declare function rfft(x: number[]): {
    re: number[];
    im: number[];
};
/**
 * Inverse real FFT: reconstruct the full conjugate-symmetric spectrum of length `n`
 * from the non-redundant half produced by {@link rfft} (bins `n/2+1..n-1` are the
 * conjugates of bins `n/2-1..1`), inverse-FFT it, and return the real parts.
 *
 * @param spec `{ re, im }` half-spectrum (bins `0..floor(n/2)`)
 * @param n Length of the reconstructed real signal
 * @returns Real-valued signal of length `n`
 */
export declare function irfft(spec: {
    re: number[];
    im: number[];
}, n: number): number[];
/**
 * Shift the zero-frequency component to the center of the spectrum (roll by `floor(n/2)`).
 *
 * Thin `number[]` public surface over the package's single roll algorithm
 * (`fftshift<T>` in `./fft.ts`) — same behavior, delegated to keep one
 * implementation.
 */
export declare function fftshift(x: number[]): number[];
/**
 * Inverse of {@link fftshift} (roll by `ceil(n/2)`).
 *
 * Thin `number[]` public surface over `ifftshift<T>` in `./fft.ts`.
 */
export declare function ifftshift(x: number[]): number[];
/**
 * DFT sample frequencies: `[0, 1, ..., ceil(n/2)-1, -floor(n/2), ..., -1] / (n*d)`.
 *
 * @param n Number of samples
 * @param d Sample spacing (default 1)
 */
export declare function fftfreq(n: number, d?: number): number[];
/**
 * DFT sample frequencies matching {@link rfft} output: `[0, 1, ..., floor(n/2)] / (n*d)`.
 *
 * @param n Number of samples
 * @param d Sample spacing (default 1)
 */
export declare function rfftfreq(n: number, d?: number): number[];
/**
 * 2-D FFT: FFT each row, then FFT each column of the result. Delegates directly to
 * the package's N-dimensional `fft`, which already performs exactly this row-then-
 * column transform when given a 2-D array.
 */
export declare function fftn(x: number[][]): {
    re: number[][];
    im: number[][];
};
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