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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* eslint-disable max-params */
'use strict';
// MODULES //
var isRowMajor = require( '@stdlib/ndarray/base/assert/is-row-major' );
// MAIN //
/**
* Generates a Hankel matrix.
*
* @private
* @param {NonNegativeInteger} M - number of indexed elements in `r` and number of rows in the output matrix
* @param {NonNegativeInteger} N - number of indexed elements in `c` and number of columns in the output matrix
* @param {Object} r - last row of the matrix
* @param {integer} strideR - stride length for `r`
* @param {NonNegativeInteger} offsetR - starting index for `r`
* @param {Object} c - first column of the matrix
* @param {integer} strideC - stride length for `c`
* @param {NonNegativeInteger} offsetC - starting index for `c`
* @param {Object} out - output array
* @param {integer} strideOut1 - stride length for the first dimension of `out`
* @param {integer} strideOut2 - stride length for the second dimension of `out`
* @param {NonNegativeInteger} offsetOut - starting index for `out`
* @returns {Object} output matrix
*
* @example
* var toAccessorArray = require( '@stdlib/array/base/to-accessor-array' );
* var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
*
* var r = [ 3.0, 4.0, 5.0 ];
* var c = [ 1.0, 2.0, 3.0 ];
* var out = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];
*
* ghankel( 3, 3, arraylike2object( toAccessorArray( r ) ), 1, 0, arraylike2object( toAccessorArray( c ) ), 1, 0, arraylike2object( toAccessorArray( out ) ), 3, 1, 0 );
* // out => [ 1.0, 2.0, 3.0, 2.0, 3.0, 4.0, 3.0, 4.0, 5.0 ]
*/
function ghankel( M, N, r, strideR, offsetR, c, strideC, offsetC, out, strideOut1, strideOut2, offsetOut ) { // eslint-disable-line max-len
var rbuf;
var cbuf;
var obuf;
var getR;
var getC;
var oset;
var do0;
var do1;
var io;
var ro;
var co;
var i0;
var i1;
var f;
rbuf = r.data;
cbuf = c.data;
obuf = out.data;
getR = r.accessors[ 0 ];
getC = c.accessors[ 0 ];
oset = out.accessors[ 1 ];
// Note on variable naming convention: S#, do#, io, i# where # corresponds to the loop number, with `0` being the innermost loop...
if ( isRowMajor( [ strideOut1, strideOut2 ] ) ) {
// Row-first iteration (inner loop walks columns):
do0 = strideOut2;
do1 = strideOut1 - ( N * strideOut2 );
io = offsetOut;
for ( i1 = 0; i1 < M; i1++ ) {
// Anti-diagonals drawn from the first column: c[i1], c[i1+1], ..., c[N-1]
f = N - i1;
if ( f < 0 ) {
f = 0;
}
co = offsetC + ( i1 * strideC );
for ( i0 = 0; i0 < f; i0++ ) {
oset( obuf, io, getC( cbuf, co ) );
co += strideC;
io += do0;
}
// Anti-diagonals drawn from the last row: r[i1+f-N+1], r[i1+f-N+2], ..., r[i1]
ro = offsetR + ( ( i1 + f - N + 1 ) * strideR );
for ( i0 = f; i0 < N; i0++ ) {
oset( obuf, io, getR( rbuf, ro ) );
ro += strideR;
io += do0;
}
io += do1;
}
return out;
}
// Column-first iteration (inner loop walks rows):
do0 = strideOut1;
do1 = strideOut2 - ( M * strideOut1 );
io = offsetOut;
for ( i1 = 0; i1 < N; i1++ ) {
// Anti-diagonals drawn from the first column: c[i1], c[i1+1], ..., c[min(N-1,i1+M-1)]
f = N - i1;
if ( f > M ) {
f = M;
}
co = offsetC + ( i1 * strideC );
for ( i0 = 0; i0 < f; i0++ ) {
oset( obuf, io, getC( cbuf, co ) );
co += strideC;
io += do0;
}
// Anti-diagonals drawn from the last row: r[1], r[2], ..., r[i1+M-N]
ro = offsetR + strideR;
for ( i0 = f; i0 < M; i0++ ) {
oset( obuf, io, getR( rbuf, ro ) );
ro += strideR;
io += do0;
}
io += do1;
}
return out;
}
// EXPORTS //
module.exports = ghankel;
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