Example 2

The program in Fig. 3.2 illustrates the use of an LAPACK95 computational routine, LA_GEQRF, which computes the QR factorization of a square matrix A ($A = QR$). (See LA_GEQRF in Section 10.2).
Remarks:

• Statement 2 includes the la_precision.mod module from LAPACK95 and sets the precision to single precision (SP) via the internal parameter WP (working precision). If SP is replaced by DP then the precision is set to double precision.
  
• Statement 3 includes the interface block of the computational routine LA_GEQRF from the f77_lapack.mod module of LAPACK95. All computational routine interfaces belong to this module.
  
• Statement 7 defines arguments A, TAU and WORK to be allocatable real single-precision arrays. The program works in complex arithmetic if REAL(WP) is replaced by COMPLEX(WP).
  
• Statements 9-10 allocate A, TAU and WORK and assign data to array A.
  
• Statements 11-13 calculate the optimal length of the work array WORK and allocate this array.
  
• Statement 14 calls LA_GEQRF to compute the QR factorization of the matrix in array A. On exit, details of the factorization are stored in array A.
  
• Statement 18 prints the contents of A.

Figure 3.2: Example program calling an LAPACK95 computational routine.