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|  | 1 | +<!-- | 
|  | 2 | +
 | 
|  | 3 | +@license Apache-2.0 | 
|  | 4 | +
 | 
|  | 5 | +Copyright (c) 2025 The Stdlib Authors. | 
|  | 6 | +
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|  | 7 | +Licensed under the Apache License, Version 2.0 (the "License"); | 
|  | 8 | +you may not use this file except in compliance with the License. | 
|  | 9 | +You may obtain a copy of the License at | 
|  | 10 | +
 | 
|  | 11 | +   http://www.apache.org/licenses/LICENSE-2.0 | 
|  | 12 | +
 | 
|  | 13 | +Unless required by applicable law or agreed to in writing, software | 
|  | 14 | +distributed under the License is distributed on an "AS IS" BASIS, | 
|  | 15 | +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | 
|  | 16 | +See the License for the specific language governing permissions and | 
|  | 17 | +limitations under the License. | 
|  | 18 | +
 | 
|  | 19 | +--> | 
|  | 20 | + | 
|  | 21 | +<!-- lint disable max-len --> | 
|  | 22 | + | 
|  | 23 | +# dgtts2 | 
|  | 24 | + | 
|  | 25 | +> Solve a system of linear equations with a tridiagonal matrix using the LU factorization computed by [dgttrf][lapack-dgttrf]. | 
|  | 26 | +
 | 
|  | 27 | +<section class="usage"> | 
|  | 28 | + | 
|  | 29 | +## Usage | 
|  | 30 | + | 
|  | 31 | +```javascript | 
|  | 32 | +var dgtts2 = require( '@stdlib/lapack/base/dgtts2' ); | 
|  | 33 | +``` | 
|  | 34 | + | 
|  | 35 | +#### dgtts2( order, itrans, N, nrhs, DL, D, DU, DU2, IPIV, B, LDB ) | 
|  | 36 | + | 
|  | 37 | +Solves a system of linear equations with a tri diagonal matrix using the LU factorization computed by [dgttrf][lapack-dgttrf]. | 
|  | 38 | + | 
|  | 39 | +```javascript | 
|  | 40 | +var Float64Array = require( '@stdlib/array/float64' ); | 
|  | 41 | +var Int32Array = require( '@stdlib/array/int32' ); | 
|  | 42 | + | 
|  | 43 | +var DL = new Float64Array( [ 0.25, 0.26666667 ] ); | 
|  | 44 | +var D = new Float64Array( [ 4.0, 3.75, 3.73333333 ] ); | 
|  | 45 | +var DU = new Float64Array( [ 1.0, 0.73333333 ] ); | 
|  | 46 | +var DU2 = new Float64Array( [ 0.0 ] ); | 
|  | 47 | +var IPIV = new Int32Array( [ 0, 1, 2 ] ); | 
|  | 48 | +var B = new Float64Array( [ 7.0, 8.0, 7.0 ] ); | 
|  | 49 | + | 
|  | 50 | +var out = dgtts2( 'column-major', 1, 3, 1, DL, D, DU, DU2, IPIV, B, 3 ); | 
|  | 51 | +// out => <Float64Array>[ ~1.44, ~1.25, ~1.55 ] | 
|  | 52 | +``` | 
|  | 53 | + | 
|  | 54 | +The function has the following parameters: | 
|  | 55 | + | 
|  | 56 | +-   **order**: storage layout. | 
|  | 57 | +-   **itrans**: specifies the form of the system of equations. | 
|  | 58 | +-   **N**: order of the matrix `A`. | 
|  | 59 | +-   **nrhs**: number of right-hand sides, i.e., the number of columns of the matrix `B`. | 
|  | 60 | +-   **DL**: multipliers that define the matrix `L`. | 
|  | 61 | +-   **D**: diagonal elements of the upper triangular matrix `U`. | 
|  | 62 | +-   **DU**: elements of the first super-diagonal of `U`. | 
|  | 63 | +-   **DU2**: elements of the second super-diagonal of `U`. | 
|  | 64 | +-   **IPIV**: vector of pivot indices. | 
|  | 65 | +-   **B**: right-hand side matrix B, overwritten by the solution matrix `X`. | 
|  | 66 | +-   **LDB**: stride of the first dimension of `B` (a.k.a., leading dimension of the matrix `B`). | 
|  | 67 | + | 
|  | 68 | +Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views. | 
|  | 69 | + | 
|  | 70 | +<!-- eslint-disable stdlib/capitalized-comments --> | 
|  | 71 | + | 
|  | 72 | +```javascript | 
|  | 73 | +var Float64Array = require( '@stdlib/array/float64' ); | 
|  | 74 | +var Int32Array = require( '@stdlib/array/int32' ); | 
|  | 75 | + | 
|  | 76 | +// Initial arrays... | 
|  | 77 | +var DL0 = new Float64Array( [ 0.0, 0.25, 0.26666667 ] ); | 
|  | 78 | +var D0 = new Float64Array( [ 0.0, 4.0, 3.75, 3.73333333 ] ); | 
|  | 79 | +var DU0 = new Float64Array( [ 0.0, 1.0, 0.73333333 ] ); | 
|  | 80 | +var DU20 = new Float64Array( [ 0.0, 0.0 ] ); | 
|  | 81 | +var IPIV0 = new Int32Array( [ 0, 0, 1, 2 ] ); | 
|  | 82 | +var B0 = new Float64Array( [ 0.0, 7.0, 8.0, 7.0 ] ); | 
|  | 83 | + | 
|  | 84 | +// Create offset views... | 
|  | 85 | +var DL = new Float64Array( DL0.buffer, DL0.BYTES_PER_ELEMENT*1 ); // start at 2nd element | 
|  | 86 | +var D = new Float64Array( D0.buffer, D0.BYTES_PER_ELEMENT*1 ); // start at 2nd element | 
|  | 87 | +var DU = new Float64Array( DU0.buffer, DU0.BYTES_PER_ELEMENT*1 ); // start at 2nd element | 
|  | 88 | +var DU2 = new Float64Array( DU20.buffer, DU20.BYTES_PER_ELEMENT*1 ); // start at 2nd element | 
|  | 89 | +var IPIV = new Int32Array( IPIV0.buffer, IPIV0.BYTES_PER_ELEMENT*1 ); // start at 2nd element | 
|  | 90 | +var B = new Float64Array( B0.buffer, B0.BYTES_PER_ELEMENT*1 ); // start at 2nd element | 
|  | 91 | + | 
|  | 92 | +dgtts2( 'column-major', 1, 3, 1, DL, D, DU, DU2, IPIV, B, 3 ); | 
|  | 93 | +// B0 => <Float64Array>[ 0.0, ~1.44, ~1.25, ~1.55 ] | 
|  | 94 | +``` | 
|  | 95 | + | 
|  | 96 | +#### dgtts2.ndarray( itrans, N, nrhs, DL, sdl, odl, D, sd, od, DU, sdu, odu, DU2, sdu2, odu2, IPIV, si, oi, B, sb1, sb2, ob ) | 
|  | 97 | + | 
|  | 98 | +Solves a system of linear equations with a tri diagonal matrix using the LU factorization computed by [dgttrf][lapack-dgttrf] and alternative indexing semantics. | 
|  | 99 | + | 
|  | 100 | +```javascript | 
|  | 101 | +var Float64Array = require( '@stdlib/array/float64' ); | 
|  | 102 | +var Int32Array = require( '@stdlib/array/int32' ); | 
|  | 103 | + | 
|  | 104 | +var DL = new Float64Array( [ 0.25, 0.26666667 ] ); | 
|  | 105 | +var D = new Float64Array( [ 4.0, 3.75, 3.73333333 ] ); | 
|  | 106 | +var DU = new Float64Array( [ 1.0, 0.73333333 ] ); | 
|  | 107 | +var DU2 = new Float64Array( [ 0.0 ] ); | 
|  | 108 | +var IPIV = new Int32Array( [ 0, 1, 2 ] ); | 
|  | 109 | +var B = new Float64Array( [ 7.0, 8.0, 7.0 ] ); | 
|  | 110 | + | 
|  | 111 | +var out = dgtts2.ndarray( 1, 3, 1, DL, 1, 0, D, 1, 0, DU, 1, 0, DU2, 1, 0, IPIV, 1, 0, B, 1, 1, 0 ); | 
|  | 112 | +// out => <Float64Array>[ ~1.44, ~1.25, ~1.55 ] | 
|  | 113 | +``` | 
|  | 114 | + | 
|  | 115 | +The function has the following parameters: | 
|  | 116 | + | 
|  | 117 | +-   **itrans**: specifies the form of the system of equations. | 
|  | 118 | +-   **N**: order of the matrix `A`. | 
|  | 119 | +-   **nrhs**: number of right-hand sides, i.e., the number of columns of the matrix `B`. | 
|  | 120 | +-   **DL**: multipliers that define the matrix `L`. | 
|  | 121 | +-   **sdl**: stride length for `DL`. | 
|  | 122 | +-   **odl**: starting index for `DL`. | 
|  | 123 | +-   **D**: diagonal elements of the upper triangular matrix `U`. | 
|  | 124 | +-   **sd**: stride length for `D`. | 
|  | 125 | +-   **od**: starting index for `D`. | 
|  | 126 | +-   **DU**: elements of the first super-diagonal of `U`. | 
|  | 127 | +-   **sdu**: stride length for `DU`. | 
|  | 128 | +-   **odu**: starting index for `DU`. | 
|  | 129 | +-   **DU2**: elements of the second super-diagonal of `U`. | 
|  | 130 | +-   **sdu2**: stride length for `DU2`. | 
|  | 131 | +-   **odu2**: starting index for `DU2`. | 
|  | 132 | +-   **IPIV**: vector of pivot indices. | 
|  | 133 | +-   **si**: stride length for `IPIV`. | 
|  | 134 | +-   **oi**: starting index for `IPIV`. | 
|  | 135 | +-   **B**: right-hand side matrix B, overwritten by the solution matrix `X`. | 
|  | 136 | +-   **sb1**: stride length for first dimension of `B`. | 
|  | 137 | +-   **sb2**: stride length for second dimension of `B`. | 
|  | 138 | +-   **ob**: starting index for `B`. | 
|  | 139 | + | 
|  | 140 | +While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, | 
|  | 141 | + | 
|  | 142 | +```javascript | 
|  | 143 | +var Float64Array = require( '@stdlib/array/float64' ); | 
|  | 144 | +var Int32Array = require( '@stdlib/array/int32' ); | 
|  | 145 | + | 
|  | 146 | +var DL = new Float64Array( [ 0.0, 0.25, 0.26666667 ] ); | 
|  | 147 | +var D = new Float64Array( [ 0.0, 4.0, 3.75, 3.73333333 ] ); | 
|  | 148 | +var DU = new Float64Array( [ 0.0, 1.0, 0.73333333 ] ); | 
|  | 149 | +var DU2 = new Float64Array( [ 0.0, 0.0 ] ); | 
|  | 150 | +var IPIV = new Int32Array( [ 0, 0, 1, 2 ] ); | 
|  | 151 | +var B = new Float64Array( [ 0.0, 7.0, 8.0, 7.0 ] ); | 
|  | 152 | + | 
|  | 153 | +var out = dgtts2.ndarray( 1, 3, 1, DL, 1, 1, D, 1, 1, DU, 1, 1, DU2, 1, 1, IPIV, 1, 1, B, 1, 1, 1 ); | 
|  | 154 | +// out => <Float64Array>[ 0.0, ~1.44, ~1.25, ~1.55 ] | 
|  | 155 | +``` | 
|  | 156 | + | 
|  | 157 | +</section> | 
|  | 158 | + | 
|  | 159 | +<!-- /.usage --> | 
|  | 160 | + | 
|  | 161 | +<section class="notes"> | 
|  | 162 | + | 
|  | 163 | +## Notes | 
|  | 164 | + | 
|  | 165 | +-   `dgtts2()` corresponds to the [LAPACK][lapack] routine [`dgtts2`][lapack-dgtts2]. | 
|  | 166 | + | 
|  | 167 | +</section> | 
|  | 168 | + | 
|  | 169 | +<!-- /.notes --> | 
|  | 170 | + | 
|  | 171 | +<section class="examples"> | 
|  | 172 | + | 
|  | 173 | +## Examples | 
|  | 174 | + | 
|  | 175 | +<!-- eslint no-undef: "error" --> | 
|  | 176 | + | 
|  | 177 | +```javascript | 
|  | 178 | +var ndarray2array = require( '@stdlib/ndarray/base/to-array' ); | 
|  | 179 | +var shape2strides = require( '@stdlib/ndarray/base/shape2strides' ); | 
|  | 180 | +var Float64Array = require( '@stdlib/array/float64' ); | 
|  | 181 | +var Int32Array = require( '@stdlib/array/int32' ); | 
|  | 182 | +var dgtts2 = require( '@stdlib/lapack/base/dgtts2' ); | 
|  | 183 | + | 
|  | 184 | +var shape = [ 3, 3 ]; | 
|  | 185 | +var order = 'row-major'; | 
|  | 186 | +var strides = shape2strides( shape, order ); | 
|  | 187 | + | 
|  | 188 | +var B = new Float64Array( [ 7.0, 8.0, 7.0, 2.0, 3.0, 4.0, 1.0, 1.5, 2.0 ] ); | 
|  | 189 | +console.log( ndarray2array( B, shape, strides, 0, order ) ); | 
|  | 190 | + | 
|  | 191 | +var DL = new Float64Array( [ 0.25, 0.26666667 ] ); | 
|  | 192 | +var D = new Float64Array( [ 4.0, 3.75, 3.73333333 ] ); | 
|  | 193 | +var DU = new Float64Array( [ 1.0, 0.73333333 ] ); | 
|  | 194 | +var DU2 = new Float64Array( [ 0.0 ] ); | 
|  | 195 | +var IPIV = new Int32Array( [ 0, 1, 2 ] ); | 
|  | 196 | + | 
|  | 197 | +var X = dgtts2( 'row-major', 1, 3, 3, DL, D, DU, DU2, IPIV, B, 3 ); | 
|  | 198 | +console.log( ndarray2array( X, shape, strides, 0, order ) ); | 
|  | 199 | +``` | 
|  | 200 | + | 
|  | 201 | +</section> | 
|  | 202 | + | 
|  | 203 | +<!-- /.examples --> | 
|  | 204 | + | 
|  | 205 | +<!-- C interface documentation. --> | 
|  | 206 | + | 
|  | 207 | +* * * | 
|  | 208 | + | 
|  | 209 | +<section class="c"> | 
|  | 210 | + | 
|  | 211 | +## C APIs | 
|  | 212 | + | 
|  | 213 | +<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. --> | 
|  | 214 | + | 
|  | 215 | +<section class="intro"> | 
|  | 216 | + | 
|  | 217 | +</section> | 
|  | 218 | + | 
|  | 219 | +<!-- /.intro --> | 
|  | 220 | + | 
|  | 221 | +<!-- C usage documentation. --> | 
|  | 222 | + | 
|  | 223 | +<section class="usage"> | 
|  | 224 | + | 
|  | 225 | +### Usage | 
|  | 226 | + | 
|  | 227 | +```c | 
|  | 228 | +TODO | 
|  | 229 | +``` | 
|  | 230 | + | 
|  | 231 | +#### TODO | 
|  | 232 | + | 
|  | 233 | +TODO. | 
|  | 234 | + | 
|  | 235 | +```c | 
|  | 236 | +TODO | 
|  | 237 | +``` | 
|  | 238 | + | 
|  | 239 | +TODO | 
|  | 240 | + | 
|  | 241 | +```c | 
|  | 242 | +TODO | 
|  | 243 | +``` | 
|  | 244 | + | 
|  | 245 | +</section> | 
|  | 246 | + | 
|  | 247 | +<!-- /.usage --> | 
|  | 248 | + | 
|  | 249 | +<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> | 
|  | 250 | + | 
|  | 251 | +<section class="notes"> | 
|  | 252 | + | 
|  | 253 | +</section> | 
|  | 254 | + | 
|  | 255 | +<!-- /.notes --> | 
|  | 256 | + | 
|  | 257 | +<!-- C API usage examples. --> | 
|  | 258 | + | 
|  | 259 | +<section class="examples"> | 
|  | 260 | + | 
|  | 261 | +### Examples | 
|  | 262 | + | 
|  | 263 | +```c | 
|  | 264 | +TODO | 
|  | 265 | +``` | 
|  | 266 | + | 
|  | 267 | +</section> | 
|  | 268 | + | 
|  | 269 | +<!-- /.examples --> | 
|  | 270 | + | 
|  | 271 | +</section> | 
|  | 272 | + | 
|  | 273 | +<!-- /.c --> | 
|  | 274 | + | 
|  | 275 | +<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. --> | 
|  | 276 | + | 
|  | 277 | +<section class="related"> | 
|  | 278 | + | 
|  | 279 | +</section> | 
|  | 280 | + | 
|  | 281 | +<!-- /.related --> | 
|  | 282 | + | 
|  | 283 | +<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> | 
|  | 284 | + | 
|  | 285 | +<section class="links"> | 
|  | 286 | + | 
|  | 287 | +[lapack]: https://www.netlib.org/lapack/explore-html/ | 
|  | 288 | + | 
|  | 289 | +[lapack-dgtts2]: https://www.netlib.org/lapack/explore-html/d2/dea/group__gtts2_gae123fb2b13f2398457e4c47f5c7f7fcd.html#gae123fb2b13f2398457e4c47f5c7f7fcd | 
|  | 290 | + | 
|  | 291 | +[lapack-dgttrf]: https://www.netlib.org/lapack/explore-html/d6/d46/group__gttrf_ga8d1e46216e6c861c89bd4328b8be52a1.html#ga8d1e46216e6c861c89bd4328b8be52a1 | 
|  | 292 | + | 
|  | 293 | +[mdn-float64array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array | 
|  | 294 | + | 
|  | 295 | +[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray | 
|  | 296 | + | 
|  | 297 | +</section> | 
|  | 298 | + | 
|  | 299 | +<!-- /.links --> | 
|  | 300 | + | 
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