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! Demonstrate expert subroutine interface with pre-allocated arrays
program example_lstsq2
use stdlib_linalg_constants, only: dp,ilp
use stdlib_linalg, only: solve_lstsq, lstsq_space, linalg_state_type
implicit none
integer, allocatable :: x(:),y(:)
real(dp), allocatable :: A(:,:),b(:),coef(:),real_space(:),singvals(:)
integer(ilp), allocatable :: int_space(:)
integer(ilp) :: lrwork,liwork,arank
! Data set
x = [1, 2, 2]
y = [5, 13, 25]
! Fit three points using a parabola, least squares method
! A = [1 x x**2]
A = reshape([[1,1,1],x,x**2],[3,3])
b = y
! Get storage sizes for the arrays and pre-allocate data
call lstsq_space(A,b,lrwork,liwork)
allocate(coef(size(x)),real_space(lrwork),int_space(liwork),singvals(minval(shape(A))))
! Solve coefficients of y = coef(1) + x*coef(2) + x^2*coef(3)
! with no internal allocations
call solve_lstsq(A,b,x=coef, &
real_storage=real_space, &
int_storage=int_space, &
singvals=singvals, &
overwrite_a=.true., &
rank=arank)
print *, 'parabola: ',coef
! parabola: -0.42857142857141695 1.1428571428571503 4.2857142857142811
print *, 'rank: ',arank
! rank: 2
end program example_lstsq2
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