usage_example.f90

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program usage_example
  use m_lookup_table
 
  implicit none
  integer, parameter   :: dp = kind(0.0d0)
 
  real(dp), parameter :: x_data(4) = [1.0_dp, 2.75_dp, 3.3_dp, 5.6_dp]
  type(lt_t)          :: my_lt
 
  print *, "This program demonstrates the usage of m_lookup_table"
  print *, ""
 
  print *, "Create a lookup table with the following options"
  print *, "   x_min    = ", x_data(1)
  print *, "   x_max    = ", x_data(4)
  print *, "   n_points = ", 20
  print *, "   n_cols   = ", 2
  my_lt = lt_create(x_data(1), x_data(4), n_points=20, n_cols=2, &
       xspacing=lt_xspacing_linear)
 
  print *, "The table input is unevenly spaced, using these x-values:"
  write(*, "(4e12.4)") x_data
  print *, ""
 
  print *, "Setting the first column to y1 = x**2"
  call lt_set_col(my_lt, 1, x_data, x_data**2)
 
  print *, "Setting the second column to y2 = sin(x)"
  call lt_set_col(my_lt, 2, x_data, sin(x_data))
 
  print *, "Adding a third column (which causes re-allocations),"
  print *, "which is set to y3 = sqrt(x)"
  call lt_add_col(my_lt, x_data, sqrt(x_data))
  print *, ""
 
  call example_1(my_lt)
  call example_2(my_lt)
  call example_3(my_lt)
  call example_4(my_lt)
  call example_5(my_lt)
 
contains
 
  subroutine example_1(lt)
    type(lt_t), intent(in) :: lt
 
    print *, "----------------------------------------"
    print *, "Example 1: Get values from a single column"
    print *, ""
    print *, "3**2 is about:       ", lt_get_col(lt, 1, 3.0_dp)
    print *, "sin(3) is about:     ", lt_get_col(lt, 2, 3.0_dp)
    print *, "sqrt(3) is about:    ", lt_get_col(lt, 3, 3.0_dp)
    print *, "----------------------------------------"
    print *, ""
  end subroutine example_1
 
  subroutine example_2(lt)
    type(lt_t), intent(in) :: lt
    type(lt_loc_t)         :: loc
 
    print *, "----------------------------------------"
    print *, "Example 2: Get values using a loc (location) object, which"
    print *, "can be faster if you look up at the same x-value often"
    print *, ""
 
    loc = lt_get_loc(my_lt, 3.0_dp)
    print *, "3**2 is about:       ", lt_get_col_at_loc(lt, 1, loc)
    print *, "sin(3) is about:     ", lt_get_col_at_loc(lt, 2, loc)
    print *, "sqrt(3) is about:    ", lt_get_col_at_loc(lt, 3, loc)
    print *, "----------------------------------------"
    print *, ""
  end subroutine example_2
 
  subroutine example_3(lt)
    type(lt_t), intent(in) :: lt
    real(dp)               :: columns(lt%n_cols)
 
    print *, "----------------------------------------"
    print *, "Example 3: Get all the columns at the same time."
    print *, "This can also be done using a loc object"
    print *, ""
 
    columns = lt_get_mcol(my_lt, 3.0_dp)
    print *, "3**2 is about:       ", columns(1)
    print *, "sin(3) is about:     ", columns(2)
    print *, "sqrt(3) is about:    ", columns(3)
    print *, "----------------------------------------"
    print *, ""
  end subroutine example_3
 
  subroutine example_4(lt)
    type(lt_t), intent(in) :: lt
 
    print *, "----------------------------------------"
    print *, "Example 4: When x > x_max or x < x_min, a lookup"
    print *, "returns y(x_max) and y(x_min), respectively"
    print *, ""
 
    print *, "The table starts at 1.0, so a lookup at 0.0 gives"
    print *, "LT_get_col(lt, 1, 0.0_dp):", lt_get_col(lt, 1, 0.0_dp)
    print *, "which is the same as"
    print *, "LT_get_col(lt, 1, 1.0_dp):", lt_get_col(lt, 1, 1.0_dp)
    print *, ""
    print *, "The table ends at 5.6, so a lookup at 10.0 gives"
    print *, "LT_get_col(lt, 1, 10.0_dp):", lt_get_col(lt, 1, 10.0_dp)
    print *, "which is the same as"
    print *, "LT_get_col(lt, 1, 5.6_dp): ", lt_get_col(lt, 1, 5.6_dp)
    print *, "----------------------------------------"
    print *, ""
  end subroutine example_4
 
  subroutine example_5(lt)
    type(lt_t), intent(in)      :: lt
    type(lt_t)                  :: new_lt
    character(len=*), parameter :: filename = "saved_table.dat"
 
    print *, "----------------------------------------"
    print *, "Example 5: You can store the lookup table in a file,"
    print *, "and read it back in. The table is stored in binary,"
    print *, "which is not always portable between machines."
 
    print *, "Storing the lookup table in    ", filename
    call lt_to_file(lt, filename)
 
    print *, "Reading in a lookup table from ", filename
    call lt_from_file(new_lt, filename)
 
    print *, ""
    print *, "The results should be the same:"
    print *, "3**2 is about:       ", lt_get_col(new_lt, 1, 3.0_dp)
    print *, "sin(3) is about:     ", lt_get_col(new_lt, 2, 3.0_dp)
    print *, "sqrt(3) is about:    ", lt_get_col(new_lt, 3, 3.0_dp)
    print *, "----------------------------------------"
    print *, ""
  end subroutine example_5
 
end program usage_example