docs: add JSDoc

lib/node_modules/@stdlib/fft/base/fftpack/ndarray/float64/docs/types/index.d.ts

@@ -27,7 +27,42 @@ import rffti = require( '@stdlib/fft/base/fftpack/ndarray/float64/rffti' );
 */
 interface Namespace {
 	/**
-	* TODO.
+	* Initializes a workspace array for performing a real-valued Fourier transform on a one-dimensional double-precision floating-point ndarray.
+	*
+	* ## Notes
+	*
+	* -   The function expects the following ndarrays:
+	*
+	*     -   a one-dimensional input ndarray.
+	*     -   a zero-dimensional ndarray containing the length of the sequence to transform.
+	*
+	* @param arrays - array-like object containing ndarrays
+	* @returns input ndarray
+	*
+	* @example
+	* var Float64Vector = require( '@stdlib/ndarray/vector/float64' );
+	* var scalar2ndarray = require( '@stdlib/ndarray/from-scalar' );
+	* var Slice = require( '@stdlib/slice/ctor' );
+	* var slice = require( '@stdlib/ndarray/slice' );
+	*
+	* var N = 8;
+	* var len = scalar2ndarray( N, {
+	*     'dtype': 'int32'
+	* });
+	*
+	* var w = new Float64Vector( ( 2*N ) + 34 );
+	*
+	* var out = ns.rffti( [ w, len ] );
+	* // returns <ndarray>
+	*
+	* var bool = ( out === w );
+	* // returns true
+	*
+	* var twiddleFactors = slice( w, new Slice( N, 2*N ) );
+	* // returns <ndarray>[ ~0.707, ~0.707, 0, 0, 0, 0, 0, 0 ]
+	*
+	* var factors = slice( w, new Slice( 2*N, ( 2*N ) + 4 ) );
+	* // returns <ndarray>[ 8, 2, 2, 4 ]
 	*/
 	rffti: typeof rffti;
 }