Added pivoting_qr_space example.

Author: loiseaujc

example/linalg/CMakeLists.txt

@@ -56,6 +56,7 @@ ADD_EXAMPLE(determinant2)
 ADD_EXAMPLE(qr)
 ADD_EXAMPLE(pivoting_qr)
 ADD_EXAMPLE(qr_space)
+ADD_EXAMPLE(pivoting_qr_space)
 ADD_EXAMPLE(cholesky)
 ADD_EXAMPLE(chol)
 ADD_EXAMPLE(expm)

example/linalg/example_pivoting_qr_space.f90

@@ -0,0 +1,25 @@
+! QR example with pre-allocated storage
+program example_pivoting_qr_space
+   use stdlib_linalg_constants, only: ilp
+   use stdlib_linalg, only: qr, qr_space, linalg_state_type
+   implicit none
+   real :: A(104, 32), Q(104, 32), R(32, 32)
+   real, allocatable :: work(:)
+   integer(ilp) :: lwork, pivots(32)
+   type(linalg_state_type) :: err
+
+   ! Create a random matrix
+   call random_number(A)
+
+   ! Prepare QR workspace
+   call qr_space(A, lwork, pivoting=.true.)
+   allocate (work(lwork))
+
+   ! Compute its QR factorization (reduced)
+   call qr(A, Q, R, pivots, storage=work, err=err)
+
+   ! Test factorization: Q*R = A
+   print *, maxval(abs(matmul(Q, R) - A(:, pivots)))
+   print *, err%print()
+
+end program example_pivoting_qr_space