Developer Reference for Intel® oneAPI Math Kernel Library for C
?opgtr
Generates the real orthogonal matrix Q determined by ?sptrd.
Syntax
lapack_int LAPACKE_sopgtr (int matrix_layout, char uplo, lapack_int n, const float* ap, const float* tau, float* q, lapack_int ldq);
lapack_int LAPACKE_dopgtr (int matrix_layout, char uplo, lapack_int n, const double* ap, const double* tau, double* q, lapack_int ldq);
Include Files
- mkl.h
Description
The routine explicitly generates the n-by-n orthogonal matrix Q formed by sptrd when reducing a packed real symmetric matrix A to tridiagonal form: A = Q*T*QT. Use this routine after a call to ?sptrd.
Input Parameters
- matrix_layout
-  
     Specifies whether matrix storage layout is row major (LAPACK_ROW_MAJOR) or column major (LAPACK_COL_MAJOR). 
- uplo
-  
     Must be 'U' or 'L'. Use the same uplo as supplied to ?sptrd. 
- n
-  
     The order of the matrix Q (n≥ 0). 
- ap, tau
-  
     Arrays ap and tau, as returned by ?sptrd. The size of ap must be at least max(1, n(n+1)/2). The size of tau must be at least max(1, n-1). 
- ldq
-  
     The leading dimension of the output array q; at least max(1, n). 
Output Parameters
- q
-  
     Array, size (size max(1, ldq*n)) . Contains the computed matrix Q. 
Return Values
This function returns a value info.
If info=0, the execution is successful.
If info = -i, the i-th parameter had an illegal value.
Application Notes
The computed matrix Q differs from an exactly orthogonal matrix by a matrix E such that ||E||2 = O(ε), where ε is the machine precision.
The approximate number of floating-point operations is (4/3)n3.
The complex counterpart of this routine is upgtr.