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Reflect the upper triangular part of a double-precision floating-point matrix
Ainto the lower triangular part of another matrixB.
npm install @stdlib/blas-ext-base-dtriu2trilAlternatively,
- To load the package in a website via a
scripttag without installation and bundlers, use the ES Module available on theesmbranch (see README). - If you are using Deno, visit the
denobranch (see README for usage intructions). - For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the
umdbranch (see README).
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To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
var dtriu2tril = require( '@stdlib/blas-ext-base-dtriu2tril' );Reflects the upper triangular part of a double-precision floating-point matrix A into the lower triangular part of another matrix B.
var Float64Array = require( '@stdlib/array-float64' );
var A = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var B = new Float64Array( [ 0.0, 0.0, 0.0, 0.0 ] );
dtriu2tril( 'row-major', 2, 2, 0, A, 2, B, 2 );
// B => <Float64Array>[ 1.0, 0.0, 2.0, 4.0 ]The function has the following parameters:
- order: storage layout.
- M: number of rows in
A. - N: number of columns in
A. - k: diagonal below which to ignore. A value of
k = 0refers to the main diagonal andk > 0refers to a diagonal above the main diagonal. Whenk > 0, the function reflects only part of the upper triangle, excluding the main diagonal and the firstk-1super-diagonals. - A: input matrix.
- LDA: stride of the first dimension of
A(a.k.a., leading dimension of the matrixA). - B: output matrix.
- LDB: stride of the first dimension of
B(a.k.a., leading dimension of the matrixB).
Setting the k parameter to a value greater than 0 excludes the main diagonal (and, for larger values, additional super-diagonals). For example, to reflect only the elements strictly above the main diagonal,
var Float64Array = require( '@stdlib/array-float64' );
var A = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var B = new Float64Array( [ 0.0, 0.0, 0.0, 0.0 ] );
dtriu2tril( 'row-major', 2, 2, 1, A, 2, B, 2 );
// B => <Float64Array>[ 0.0, 0.0, 2.0, 0.0 ]Note that indexing is relative to the first index. To introduce an offset, use typed array views.
var Float64Array = require( '@stdlib/array-float64' );
// Initial arrays...
var A0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
var B0 = new Float64Array( 5 );
// Create offset views...
var A1 = new Float64Array( A0.buffer, A0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var B1 = new Float64Array( B0.buffer, B0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
dtriu2tril( 'row-major', 2, 2, 0, A1, 2, B1, 2 );
// B0 => <Float64Array>[ 0.0, 2.0, 0.0, 3.0, 5.0 ]Reflects the upper triangular part of a double-precision floating-point matrix A into the lower triangular part of another matrix B using alternative indexing semantics.
var Float64Array = require( '@stdlib/array-float64' );
var A = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var B = new Float64Array( [ 0.0, 0.0, 0.0, 0.0 ] );
dtriu2tril.ndarray( 2, 2, 0, A, 2, 1, 0, B, 2, 1, 0 );
// B => <Float64Array>[ 1.0, 0.0, 2.0, 4.0 ]The function has the following parameters:
- M: number of rows in
A. - N: number of columns in
A. - k: diagonal below which to ignore.
- A: input matrix.
- sa1: stride of the first dimension of
A. - sa2: stride of the second dimension of
A. - oa: starting index for
A. - B: output matrix.
- sb1: stride of the first dimension of
B. - sb2: stride of the second dimension of
B. - ob: starting index for
B.
While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example,
var Float64Array = require( '@stdlib/array-float64' );
var A = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var B = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
dtriu2tril.ndarray( 2, 2, 0, A, 2, 1, 0, B, 2, 1, 2 );
// B => <Float64Array>[ 0.0, 0.0, 1.0, 0.0, 2.0, 4.0 ]- Elements outside of the reflected region are left unchanged.
var ndarray2array = require( '@stdlib/ndarray-base-to-array' );
var uniform = require( '@stdlib/random-array-discrete-uniform' );
var numel = require( '@stdlib/ndarray-base-numel' );
var shape2strides = require( '@stdlib/ndarray-base-shape2strides' );
var dtriu2tril = require( '@stdlib/blas-ext-base-dtriu2tril' );
var shape = [ 5, 8 ];
var order = 'row-major';
var strides = shape2strides( shape, order );
var N = numel( shape );
var A = uniform( N, -10, 10, {
'dtype': 'float64'
});
console.log( ndarray2array( A, shape, strides, 0, order ) );
var B = uniform( N, -10, 10, {
'dtype': 'float64'
});
var shapeB = [ shape[ 1 ], shape[ 0 ] ];
var stridesB = shape2strides( shapeB, order );
console.log( ndarray2array( B, shapeB, stridesB, 0, order ) );
dtriu2tril( order, shape[ 0 ], shape[ 1 ], 0, A, strides[ 0 ], B, stridesB[ 0 ] );
console.log( ndarray2array( B, shapeB, stridesB, 0, order ) );#include "stdlib/blas/ext/base/dtriu2tril.h"Reflects the upper triangular part of a double-precision floating-point matrix A into the lower triangular part of another matrix B.
#include "stdlib/blas/base/shared.h"
const double A[] = { 1.0, 2.0, 3.0, 4.0 };
double B[] = { 0.0, 0.0, 0.0, 0.0 };
stdlib_strided_dtriu2tril( CblasRowMajor, 2, 2, 0, A, 2, B, 2 );The function accepts the following arguments:
- layout:
[in] CBLAS_LAYOUTstorage layout. - M:
[in] CBLAS_INTnumber of rows inA. - N:
[in] CBLAS_INTnumber of columns inA. - k:
[in] CBLAS_INTdiagonal below which to ignore. - A:
[in] double*input matrix. - LDA:
[in] CBLAS_INTstride of the first dimension ofA(a.k.a., leading dimension of the matrixA). - B:
[out] double*output matrix. - LDB:
[in] CBLAS_INTstride of the first dimension ofB(a.k.a., leading dimension of the matrixB).
void API_SUFFIX(stdlib_strided_dtriu2tril)( const CBLAS_LAYOUT layout, const CBLAS_INT M, const CBLAS_INT N, const CBLAS_INT k, const double *A, const CBLAS_INT LDA, double *B, const CBLAS_INT LDB );Reflects the upper triangular part of a double-precision floating-point matrix A into the lower triangular part of another matrix B using alternative indexing semantics.
const double A[] = { 1.0, 2.0, 3.0, 4.0 };
double B[] = { 0.0, 0.0, 0.0, 0.0 };
stdlib_strided_dtriu2tril_ndarray( 2, 2, 0, A, 2, 1, 0, B, 2, 1, 0 );The function accepts the following arguments:
- M:
[in] CBLAS_INTnumber of rows inA. - N:
[in] CBLAS_INTnumber of columns inA. - k:
[in] CBLAS_INTdiagonal below which to ignore. - A:
[in] double*input matrix. - sa1:
[in] CBLAS_INTstride of the first dimension ofA. - sa2:
[in] CBLAS_INTstride of the second dimension ofA. - oa:
[in] CBLAS_INTstarting index forA. - B:
[out] double*output matrix. - sb1:
[in] CBLAS_INTstride of the first dimension ofB. - sb2:
[in] CBLAS_INTstride of the second dimension ofB. - ob:
[in] CBLAS_INTstarting index forB.
void API_SUFFIX(stdlib_strided_dtriu2tril_ndarray)( const CBLAS_INT M, const CBLAS_INT N, const CBLAS_INT k, const double *A, const CBLAS_INT strideA1, const CBLAS_INT strideA2, const CBLAS_INT offsetA, double *B, const CBLAS_INT strideB1, const CBLAS_INT strideB2, const CBLAS_INT offsetB );#include "stdlib/blas/ext/base/dtriu2tril.h"
#include "stdlib/blas/base/shared.h"
#include <stdio.h>
int main( void ) {
// Define a 3x3 input matrix stored in row-major order:
const double A[ 3*3 ] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 };
// Define a 3x3 output matrix:
double B[ 3*3 ] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };
// Specify the number of elements along each dimension of `A`:
const CBLAS_INT M = 3;
const CBLAS_INT N = 3;
// Reflect the upper triangular part of `A` into the lower triangular part of `B`:
stdlib_strided_dtriu2tril( CblasRowMajor, M, N, 0, A, N, B, N );
// Print the result:
for ( int i = 0; i < M; i++ ) {
for ( int j = 0; j < N; j++ ) {
printf( "B[ %i,%i ] = %lf\n", i, j, B[ (i*N)+j ] );
}
}
// Reflect the upper triangular part of `A` (above the first super-diagonal) into `B` using alternative indexing semantics:
stdlib_strided_dtriu2tril_ndarray( M, N, 1, A, N, 1, 0, B, N, 1, 0 );
// Print the result:
for ( int i = 0; i < M; i++ ) {
for ( int j = 0; j < N; j++ ) {
printf( "B[ %i,%i ] = %lf\n", i, j, B[ (i*N)+j ] );
}
}
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