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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.
*/
'use strict';
// MODULES //
var isRowMajor = require( '@stdlib/ndarray/base/assert/is-row-major' );
var gfill = require( '@stdlib/blas/ext/base/gfill' ).ndarray;
// MAIN //
/**
* Generates a Vandermonde matrix using accessor arrays.
*
* @private
* @param {integer} mode - mode indicating whether to generate increasing or decreasing powers
* @param {NonNegativeInteger} M - number of rows in `out`
* @param {NonNegativeInteger} N - number of columns in `out`
* @param {Object} x - input array object
* @param {integer} sx - stride length for `x`
* @param {NonNegativeInteger} ox - starting index for `x`
* @param {Object} out - output matrix object
* @param {integer} so1 - stride length for the first dimension of `out`
* @param {integer} so2 - stride length for the second dimension of `out`
* @param {NonNegativeInteger} oo - starting index for `out`
* @returns {Collection} output matrix
*
* @example
* var toAccessorArray = require( '@stdlib/array/base/to-accessor-array' );
* var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
*
* var x = [ 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 ];
*
* gvander( 1, 3, 3, arraylike2object( toAccessorArray( x ) ), 1, 0, arraylike2object( toAccessorArray( out ) ), 3, 1, 0 );
*
* console.log( out );
* // => [ 1.0, 1.0, 1.0, 1.0, 2.0, 4.0, 1.0, 3.0, 9.0 ]
*/
function gvander( mode, M, N, x, sx, ox, out, so1, so2, oo ) {
var xbuf;
var obuf;
var xget;
var oget;
var oset;
var isrm;
var tmp;
var do0;
var do1;
var S0;
var S1;
var io;
var ix;
var i0;
var i1;
var v;
xbuf = x.data;
obuf = out.data;
xget = x.accessors[ 0 ];
oget = out.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...
isrm = isRowMajor( [ so1, so2 ] );
if ( isrm && mode > 0 ) {
// Row-major, increasing: x^0, x^1, ..., x^(N-1)
S0 = N;
S1 = M;
do0 = so2;
do1 = so1 - ( S0*so2 );
io = oo;
ix = ox;
for ( i1 = 0; i1 < S1; i1++ ) {
v = xget( xbuf, ix );
oset( obuf, io, 1.0 );
tmp = 1.0;
io += do0;
for ( i0 = 1; i0 < S0; i0++ ) {
tmp *= v;
oset( obuf, io, tmp );
io += do0;
}
ix += sx;
io += do1;
}
} else if ( isrm ) {
// Row-major, decreasing: x^(N-1), x^(N-2), ..., x^0
S0 = N;
S1 = M;
do0 = so2;
do1 = so1 + ( S0*so2 );
io = oo + ( ( S0-1 ) * do0 );
ix = ox;
for ( i1 = 0; i1 < S1; i1++ ) {
v = xget( xbuf, ix );
oset( obuf, io, 1.0 );
tmp = 1.0;
io -= do0;
for ( i0 = 1; i0 < S0; i0++ ) {
tmp *= v;
oset( obuf, io, tmp );
io -= do0;
}
ix += sx;
io += do1;
}
} else if ( mode > 0 ) {
// Column-major, increasing: column j contains x^j
S0 = M;
S1 = N;
do0 = so1;
do1 = so2 - ( S0*so1 );
io = oo;
gfill( S0, 1.0, obuf, do0, io );
io += so2;
for ( i1 = 1; i1 < S1; i1++ ) {
ix = ox;
for ( i0 = 0; i0 < S0; i0++ ) {
oset( obuf, io, oget( obuf, io - so2 ) * xget( xbuf, ix ) );
ix += sx;
io += do0;
}
io += do1;
}
} else {
// Column-major, decreasing: column 0 contains x^(N-1), last column all ones
S0 = M;
S1 = N;
gfill( S0, 1.0, obuf, so1, oo + ( ( S1-1 ) * so2 ) );
for ( i1 = S1 - 2; i1 >= 0; i1-- ) {
io = oo + ( i1 * so2 );
ix = ox;
for ( i0 = 0; i0 < S0; i0++ ) {
oset( obuf, io, oget( obuf, io + so2 ) * xget( xbuf, ix ) );
ix += sx;
io += so1;
}
}
}
return obuf;
}
// EXPORTS //
module.exports = gvander;
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