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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 isLayout = require( '@stdlib/blas/base/assert/is-layout' );
var isTransposeOperation = require( '@stdlib/blas/base/assert/is-transpose-operation' );
var isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major-string' );
var max = require( '@stdlib/math/base/special/fast/max' );
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.
*
* ## 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} order - storage layout
* @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 {Float64Array} D - diagonal of `A`
* @param {Float64Array} DU - super-diagonal of `A`
* @param {Float64Array} X - input matrix `X`
* @param {PositiveInteger} LDX - stride of the first dimension of `X` (a.k.a., leading dimension of the matrix `X`)
* @param {number} beta - scalar beta
* @param {Float64Array} B - input/output matrix `B`
* @param {PositiveInteger} LDB - stride of the first dimension of `B` (a.k.a., leading dimension of the matrix `B`)
* @throws {TypeError} first argument must be a valid order
* @throws {TypeError} second argument must be a valid transpose operation
* @throws {RangeError} third argument must be a nonnegative integer
* @throws {RangeError} fourth argument must be a nonnegative integer
* @throws {RangeError} tenth argument must be greater than or equal to max(1,N) when column-major or max(1,NRHS) when row-major
* @throws {RangeError} thirteenth argument must be greater than or equal to max(1,N) when column-major or max(1,NRHS) when row-major
* @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( 'column-major', 'no-transpose', 3, 1, 1.0, DL, D, DU, X, 3, 0.0, B, 3 );
* // B => <Float64Array>[ 3.0, 5.0, 5.0 ]
*/
function dlagtm( order, trans, N, NRHS, alpha, DL, D, DU, X, LDX, beta, B, LDB ) { // eslint-disable-line max-len, max-params
var sx1;
var sx2;
var sb1;
var sb2;
if ( !isLayout( order ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a valid order. Value: `%s`.', order ) );
}
if ( !isTransposeOperation( trans ) ) {
throw new TypeError( format( 'invalid argument. Second argument must be a valid transpose operation. Value: `%s`.', trans ) );
}
if ( N < 0 ) {
throw new RangeError( format( 'invalid argument. Third argument must be a nonnegative integer. Value: `%d`.', N ) );
}
if ( NRHS < 0 ) {
throw new RangeError( format( 'invalid argument. Fourth argument must be a nonnegative integer. Value: `%d`.', NRHS ) );
}
if ( isColumnMajor( order ) ) {
if ( LDX < max( 1, N ) ) {
throw new RangeError( format( 'invalid argument. Tenth argument must be greater than or equal to max(1,%d). Value: `%d`.', N, LDX ) );
}
if ( LDB < max( 1, N ) ) {
throw new RangeError( format( 'invalid argument. Thirteenth argument must be greater than or equal to max(1,%d). Value: `%d`.', N, LDB ) );
}
sx1 = 1;
sx2 = LDX;
sb1 = 1;
sb2 = LDB;
} else { // order === 'row-major'
if ( LDX < max( 1, NRHS ) ) {
throw new RangeError( format( 'invalid argument. Tenth argument must be greater than or equal to max(1,%d). Value: `%d`.', NRHS, LDX ) );
}
if ( LDB < max( 1, NRHS ) ) {
throw new RangeError( format( 'invalid argument. Thirteenth argument must be greater than or equal to max(1,%d). Value: `%d`.', NRHS, LDB ) );
}
sx1 = LDX;
sx2 = 1;
sb1 = LDB;
sb2 = 1;
}
return base( trans, N, NRHS, alpha, DL, 1, 0, D, 1, 0, DU, 1, 0, X, sx1, sx2, 0, beta, B, sb1, sb2, 0 ); // eslint-disable-line max-len
}
// EXPORTS //
module.exports = dlagtm;
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