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program do_concurrent_13
integer, parameter :: Nx = 600, Ny = 450, n_max = 255, dp=kind(0.d0)
real(dp), parameter :: xcenter = -0.5_dp, ycenter = 0.0_dp, &
width = 4, height = 3, dx_di = width/Nx, dy_dj = -height/Ny, &
x_offset = xcenter - (Nx+1)*dx_di/2, y_offset = ycenter - (Ny+1)*dy_dj/2
real(dp) :: x, y, x_0, y_0, x_sqr, y_sqr, wtime
integer :: i, j, n, image(Nx, Ny)
do concurrent (j = 1:Ny) shared(image) local(i, x, y, x_0, y_0, x_sqr, y_sqr, n)
y_0 = y_offset + dy_dj * j
do i = 1, Nx
x_0 = x_offset + dx_di * i
x = 0; y = 0; n = 0
do
x_sqr = x ** 2; y_sqr = y ** 2
if (x_sqr + y_sqr > 4 .or. n == n_max) then
image(i,j) = 255-n
exit
end if
y = y_0 + 2 * x * y
x = x_0 + x_sqr - y_sqr
n = n + 1
end do
end do
end do
print *, sum(image)
if ( sum(image) /= 59157126 ) error stop
end program
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