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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 stride2offset = require( '@stdlib/strided/base/stride2offset' );
var format = require( '@stdlib/string/format' );
var isNorm = require( './is_norm.js' );
var base = require( './base.js' );
// MAIN //
/**
* Returns the value of the one-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a real tridiagonal matrix `A`.
*
* @param {string} norm - specifies the norm type
* @param {NonNegativeInteger} N - order of the matrix
* @param {Float64Array} DL - sub-diagonal elements (length N-1)
* @param {integer} strideDL - stride length for `DL`
* @param {Float64Array} D - diagonal elements (length N)
* @param {integer} strideD - stride length for `D`
* @param {Float64Array} DU - super-diagonal elements (length N-1)
* @param {integer} strideDU - stride length for `DU`
* @throws {TypeError} first argument must be a valid norm type
* @returns {number} matrix norm
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var DL = new Float64Array( [ 1.0, 2.0, 3.0 ] );
* var D = new Float64Array( [ 4.0, 5.0, 6.0, 7.0 ] );
* var DU = new Float64Array( [ 1.0, 1.0, 1.0 ] );
*
* var norm = dlangt( 'M', 4, DL, 1, D, 1, DU, 1 );
* // returns 7.0
*/
function dlangt( norm, N, DL, strideDL, D, strideD, DU, strideDU ) {
if ( !isNorm( norm ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a valid norm type. Value: `%s`.', norm ) );
}
if ( N <= 0 ) {
return 0.0;
}
return base( norm, N, DL, strideDL, stride2offset( N - 1, strideDL ), D, strideD, stride2offset( N, strideD ), DU, strideDU, stride2offset( N - 1, strideDU ) );
}
// EXPORTS //
module.exports = dlangt;
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