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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 isTransposeOperation = require( '@stdlib/blas/base/assert/is-transpose-operation' );
var format = require( '@stdlib/string/format' );
var base = require( './base.js' );
// MAIN //
/**
* Performs a matrix-matrix product of the form `B := α*op(A)*X + β*B` where `op(A)` is either `op(A) = A` or `op(A) = A^T`, `α` and `β` are scalars, and `A` is a tridiagonal matrix, using alternative indexing semantics.
*
* ## Notes
*
* - `DL` should have `N-1` indexed elements representing the sub-diagonal of `A`.
* - `D` should have `N` indexed elements representing the diagonal of `A`.
* - `DU` should have `N-1` indexed elements representing the super-diagonal of `A`.
* - As `A` is a real matrix, a conjugate transpose is equivalent to a transpose.
* - `alpha` must be `0`, `1`, or `-1`; otherwise, it is assumed to be `0`.
* - `beta` must be `0`, `1`, or `-1`; otherwise, it is assumed to be `1`.
* - `B` is overwritten and returned; `DL`, `D`, `DU`, and `X` are left unchanged.
*
* @param {string} trans - specifies whether `A` should be transposed, conjugate-transposed, or not transposed
* @param {NonNegativeInteger} N - order of the matrix `A`
* @param {NonNegativeInteger} NRHS - number of right hand sides (columns of `X` and `B`)
* @param {number} alpha - scalar alpha
* @param {Float64Array} DL - sub-diagonal of `A`
* @param {integer} strideDL - stride length for `DL`
* @param {NonNegativeInteger} offsetDL - starting index of `DL`
* @param {Float64Array} D - diagonal of `A`
* @param {integer} strideD - stride length for `D`
* @param {NonNegativeInteger} offsetD - starting index of `D`
* @param {Float64Array} DU - super-diagonal of `A`
* @param {integer} strideDU - stride length for `DU`
* @param {NonNegativeInteger} offsetDU - starting index of `DU`
* @param {Float64Array} X - input matrix `X`
* @param {integer} strideX1 - stride of the first dimension of `X`
* @param {integer} strideX2 - stride of the second dimension of `X`
* @param {NonNegativeInteger} offsetX - starting index of `X`
* @param {number} beta - scalar beta
* @param {Float64Array} B - input/output matrix `B`
* @param {integer} strideB1 - stride of the first dimension of `B`
* @param {integer} strideB2 - stride of the second dimension of `B`
* @param {NonNegativeInteger} offsetB - starting index of `B`
* @throws {TypeError} first argument must be a valid transpose operation
* @throws {RangeError} second argument must be a nonnegative integer
* @throws {RangeError} third argument must be a nonnegative integer
* @returns {Float64Array} `B`
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var DL = new Float64Array( [ 1.0, 1.0 ] );
* var D = new Float64Array( [ 2.0, 3.0, 4.0 ] );
* var DU = new Float64Array( [ 1.0, 1.0 ] );
* var X = new Float64Array( [ 1.0, 1.0, 1.0 ] );
* var B = new Float64Array( [ 0.0, 0.0, 0.0 ] );
*
* dlagtm( 'no-transpose', 3, 1, 1.0, DL, 1, 0, D, 1, 0, DU, 1, 0, X, 1, 3, 0, 0.0, B, 1, 3, 0 );
* // B => <Float64Array>[ 3.0, 5.0, 5.0 ]
*/
function dlagtm( trans, N, NRHS, alpha, DL, strideDL, offsetDL, D, strideD, offsetD, DU, strideDU, offsetDU, X, strideX1, strideX2, offsetX, beta, B, strideB1, strideB2, offsetB ) { // eslint-disable-line max-len, max-params
if ( !isTransposeOperation( trans ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a valid transpose operation. Value: `%s`.', trans ) );
}
if ( N < 0 ) {
throw new RangeError( format( 'invalid argument. Second argument must be a nonnegative integer. Value: `%d`.', N ) );
}
if ( NRHS < 0 ) {
throw new RangeError( format( 'invalid argument. Third argument must be a nonnegative integer. Value: `%d`.', NRHS ) );
}
return base( trans, N, NRHS, alpha, DL, strideDL, offsetDL, D, strideD, offsetD, DU, strideDU, offsetDU, X, strideX1, strideX2, offsetX, beta, B, strideB1, strideB2, offsetB ); // eslint-disable-line max-len
}
// EXPORTS //
module.exports = dlagtm;
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