Fortran Best Practices: Floating Point Numbers comparison

[band-a-prend]

The Floating Point Number section of Fortran Best Practices could be extended with 2 subsections:

1. comparison of two real numbers;
2. undesirability of using real as iterator within do loops (it was deprecated in Fortran95 standard).

The motivation.
It's common problem for all programming languages when beginner programmer tries to compare fooating points numbers especially using if statement. It would be usefull to demonstrate more accurate approaches (with use of intrinsic procedures?) of comparing numbers to avoid accuracy and computational issues.

The second problem comes from first one and could results in computational issues.

[PANKAJ11111111]

Please give chance i fix this problem

[saikarna913]

real(dp) :: tol
tol = 10 * epsilon(1.0_dp)

real(dp), parameter :: tol = 1.0e-10_dp
if (abs(x - y) < tol) then
   print *, "Effectively Equal"
else
   print *, "Not Equal"
end if

Floating-point numbers like 0.1 cannot be represented exactly in binary because their binary form is infinite and repeating. Due to the limited precision of floating-point formats (like 32-bit or 64-bit), these numbers are rounded off to fit within the constrained number of bits. This rounding can lead to small errors in representation and calculations. so it is better to add tolerance and check whether the numbers are close enough.

for second
Use integer iterators and convert them to floating point within the loop:

integer :: i
real(dp) :: step, value
step = 0.1_dp
do i = 0, 10
   value = i * step
   print *, value
end do

[saikarna913]

@band-a-prend do you want me to write this in the documentation website