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program example_exponential_pdf
use stdlib_random, only: random_seed
use stdlib_stats_distribution_exponential, only: exp_pdf => pdf_exp, &
rexp => rvs_exp
implicit none
real, dimension(2, 3, 4) :: x, loc, scale
real :: xsum
complex :: cloc, cscale
integer :: seed_put, seed_get, i
seed_put = 1234567
call random_seed(seed_put, seed_get)
! probability density at x=1.0 with loc=0 and scale=1.0
print *, exp_pdf(1.0, 0.0, 1.0)
! 0.367879450
! probability density at x=1.0 with lambda=1.0
print *, exp_pdf(1.0, 1.0)
! 0.367879450
! probability density at x=2.0 with lambda=2.0
print *, exp_pdf(2.0, 2.0)
! 3.66312787E-02
! probability density at x=2.0 with loc=0.0 and scale=0.5 (lambda=2.0)
print *, exp_pdf(2.0, 0.0, 0.5)
! 3.66312787E-02
! probability density at x=1.5 with loc=0.5 and scale=0.5 (lambda=2.0)
print *, exp_pdf(2.5, 0.5, 0.5)
! 3.66312787E-02
! probability density at x=2.0 with loc=0.0 and scale=-1.0 (out of range)
print *, exp_pdf(2.0, 0.0, -1.0)
! NaN
! standard exponential random variates array
x = reshape(rexp(0.0, 2.0, 24), [2, 3, 4])
! a rank-3 exponential probability density
loc(:, :, :) = 0.0
scale(:, :, :) = 2.0
print *, exp_pdf(x, loc, scale)
! 0.349295378 0.332413018 0.470253497 0.443498343 0.317152828
! 0.208242029 0.443112582 8.07073265E-02 0.245337561 0.436016470
! 7.14025944E-02 5.33841923E-02 0.322308093 0.264558554 0.212898195
! 0.100339092 0.226891592 0.444002301 9.91026312E-02 3.87373678E-02
! 3.11400592E-02 0.349431813 0.482774824 0.432669312
! probability density array where scale<=0.0 for certain elements (loc = 0.0)
print *, exp_pdf([1.0, 1.0, 1.0], [0.0, 0.0, 0.0], [1.0, 0.0, -1.0])
! 0.367879450 NaN NaN
! `pdf_exp` is pure and, thus, can be called concurrently
xsum = 0.0
do concurrent (i=1:size(x,3))
xsum = xsum + sum(exp_pdf(x(:,:,i), loc(:,:,i), scale(:,:,i)))
end do
print *, xsum
! 6.45566940
! complex exponential probability density function at (1.5, 0.0, 1.0) with real part
! of scale=1.0 and imaginary part of scale=0.5
cloc = (0.0, 0.0)
cscale = (1.0, 0.5)
print *, exp_pdf((1.5, 1.0), cloc, cscale)
! 6.03947677E-02
! As above, but with scale%re < 0
cloc = (0.0, 0.0)
cscale = (-1.0, 2.0)
print *, exp_pdf((1.5, 1.0), cloc, cscale)
! NaN
end program example_exponential_pdf
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