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* @license Apache-2.0
*
* Copyright (c) 2025 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';
/**
* LAPACK routine to compute the Schur factorization of a real 2-by-2 nonsymmetric matrix `A` in standard form.
*
* Given a real 2×2 matrix:
*
* ```tex
* \begin{bmatrix}
* A & B \\
* C & D
* \end{bmatrix}
* ```
*
* this routine computes an orthogonal matrix:
*
* ```tex
* \begin{bmatrix}
* \text{CS} & \text{SN} \\
* -\text{SN} & \text{CS}
* \end{bmatrix}
* ```
*
* such that the matrix is reduced to Schur (quasi-triangular) form:
*
* ```tex
* \begin{bmatrix}
* \text{AA} & \text{BB} \\
* \text{CC} & \text{DD}
* \end{bmatrix}
* ```
*
* where either:
*
* - `CC` = 0, `AA` and `DD` are the real eigenvalues of the matrix.
* - `AA` = `DD` and `BB * CC` < 0, `AA + sqrt( BB * CC )` and `AA - sqrt( BB * CC )` are the complex conjugate eigenvalues.
*
* @module @stdlib/lapack/base/dlanv2
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var dlanv2 = require( '@stdlib/lapack/base/dlanv2' );
*
* var A = new Float64Array( [ 4.0 ] );
* var B = new Float64Array( [ -5.0 ] );
* var C = new Float64Array( [ 2.0 ] );
* var D = new Float64Array( [ -3.0 ] );
* var RT1R = new Float64Array( 1 );
* var RT1I = new Float64Array( 1 );
* var RT2R = new Float64Array( 1 );
* var RT2I = new Float64Array( 1 );
* var CS = new Float64Array( 1 );
* var SN = new Float64Array( 1 );
*
* dlanv2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN );
* // A => <Float64Array>[ 2.0 ]
* // B => <Float64Array>[ -7.0 ]
* // C => <Float64Array>[ 0.0 ]
* // D => <Float64Array>[ -1.0 ]
* // RT1R => <Float64Array>[ 2.0 ]
* // RT1I => <Float64Array>[ 0.0 ]
* // RT2R => <Float64Array>[ -1.0 ]
* // RT2I => <Float64Array>[ 0.0 ]
* // CS => <Float64Array>[ ~0.93 ]
* // SN => <Float64Array>[ ~0.34 ]
*/
// MODULES //
var join = require( 'path' ).join;
var tryRequire = require( '@stdlib/utils/try-require' );
var isError = require( '@stdlib/assert/is-error' );
var main = require( './main.js' );
// MAIN //
var dlanv2;
var tmp = tryRequire( join( __dirname, './native.js' ) );
if ( isError( tmp ) ) {
dlanv2 = main;
} else {
dlanv2 = tmp;
}
// EXPORTS //
module.exports = dlanv2;
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