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| 1 | +/* |
| 2 | + LAPACKE Example : Calling DGELS using row-major layout |
| 3 | + ===================================================== |
| 4 | +
|
| 5 | + The program computes the solution to the system of linear |
| 6 | + equations with a square matrix A and multiple |
| 7 | + right-hand sides B, where A is the coefficient matrix |
| 8 | + and b is the right-hand side matrix: |
| 9 | +
|
| 10 | + Description |
| 11 | + =========== |
| 12 | +
|
| 13 | + In this example, we wish solve the least squares problem min_x || B - Ax || |
| 14 | + for two right-hand sides using the LAPACK routine DGELS. For input we will |
| 15 | + use the 5-by-3 matrix |
| 16 | +
|
| 17 | + ( 1 1 1 ) |
| 18 | + ( 2 3 4 ) |
| 19 | + A = ( 3 5 2 ) |
| 20 | + ( 4 2 5 ) |
| 21 | + ( 5 4 3 ) |
| 22 | + and the 5-by-2 matrix |
| 23 | +
|
| 24 | + ( -10 -3 ) |
| 25 | + ( 12 14 ) |
| 26 | + B = ( 14 12 ) |
| 27 | + ( 16 16 ) |
| 28 | + ( 18 16 ) |
| 29 | + We will first store the input matrix as a static C two-dimensional array, |
| 30 | + which is stored in row-major layout, and let LAPACKE handle the work space |
| 31 | + array allocation. The LAPACK base name for this function is gels, and we |
| 32 | + will use double precision (d), so the LAPACKE function name is LAPACKE_dgels. |
| 33 | +
|
| 34 | + thus lda=3 and ldb=2. The output for each right hand side is stored in b as |
| 35 | + consecutive vectors of length 3. The correct answer for this problem is |
| 36 | + the 3-by-2 matrix |
| 37 | +
|
| 38 | + ( 2 1 ) |
| 39 | + ( 1 1 ) |
| 40 | + ( 1 2 ) |
| 41 | +
|
| 42 | + A complete C program for this example is given below. Note that when the arrays |
| 43 | + are passed to the LAPACK routine, they must be dereferenced, since LAPACK is |
| 44 | + expecting arrays of type double *, not double **. |
| 45 | +
|
| 46 | +
|
| 47 | + LAPACKE Interface |
| 48 | + ================= |
| 49 | +
|
| 50 | + LAPACKE_dgels (row-major, high-level) Example Program Results |
| 51 | +
|
| 52 | + -- LAPACKE Example routine -- |
| 53 | + -- LAPACK is a software package provided by Univ. of Tennessee, -- |
| 54 | + -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
| 55 | +*/ |
| 56 | +/* Calling DGELS using row-major layout */ |
| 57 | + |
| 58 | +/* Includes */ |
| 59 | +#include <stdio.h> |
| 60 | +#include <lapacke_64.h> |
| 61 | +#include "lapacke_example_aux.h" |
| 62 | + |
| 63 | +/* Main program */ |
| 64 | +int main (int argc, const char * argv[]) |
| 65 | +{ |
| 66 | + /* Locals */ |
| 67 | + double A[5][3] = {{1,1,1},{2,3,4},{3,5,2},{4,2,5},{5,4,3}}; |
| 68 | + double b[5][2] = {{-10,-3},{12,14},{14,12},{16,16},{18,16}}; |
| 69 | + int64_t info,m,n,lda,ldb,nrhs; |
| 70 | + |
| 71 | + /* Initialization */ |
| 72 | + m = 5; |
| 73 | + n = 3; |
| 74 | + nrhs = 2; |
| 75 | + lda = 3; |
| 76 | + ldb = 2; |
| 77 | + |
| 78 | + /* Print Entry Matrix */ |
| 79 | + print_matrix_rowmajor_64( "Entry Matrix A", m, n, *A, lda ); |
| 80 | + /* Print Right Rand Side */ |
| 81 | + print_matrix_rowmajor_64( "Right Hand Side b", n, nrhs, *b, ldb ); |
| 82 | + printf( "\n" ); |
| 83 | + |
| 84 | + /* Executable statements */ |
| 85 | + printf( "LAPACKE_dgels_64 (row-major, high-level) Example Program Results\n" ); |
| 86 | + /* Solve least squares problem*/ |
| 87 | + info = LAPACKE_dgels_64(LAPACK_ROW_MAJOR,'N',m,n,nrhs,*A,lda,*b,ldb); |
| 88 | + |
| 89 | + /* Print Solution */ |
| 90 | + print_matrix_rowmajor_64( "Solution", n, nrhs, *b, ldb ); |
| 91 | + printf( "\n" ); |
| 92 | + exit( 0 ); |
| 93 | +} /* End of LAPACKE_dgels Example */ |
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