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Determine if Two Values Are Nearly Equal

Syntax
Purpose
x
y
r
a
e
Example

Syntax
e = near_equal_f(x, y, r, a)

Purpose
Returns true, if x is nearly equal to y and false otherwise.

x
The argument x has prototype
     double precision x
y
The argument y has prototype
     double precision y
r
The relative error criteria r has prototype
     double precision r
 It must be greater than or equal zero. The relative error condition is satisfied if @[@ | x - y | \leq r ( |x| + |y| ) @]@ where @(@ \leq @)@ denotes less than or equal.

a
The absolute error criteria a has prototype
     double precision a
 It must be greater than or equal zero. The absolute error condition is satisfied if @[@ | x - y | \leq a @]@

e
The return value e has prototype
     logical e
 If either the relative or absolute error condition is satisfied, it is true. Otherwise, it is false.

Example
The following is an example and test of near_equal_f. It returns true if the test succeeds and false if it fails. 
 
     c Use integer for return value so that this function is callable by C
           integer function ok_near_equal_f()
           double precision x, y, r, a
           logical near_equal_f
           external near_equal_f
           x = 1.1
           y = 1.2
           r = .1
           a = 0.
           if( near_equal_f(x, y, r, a) ) then
                 ok_near_equal_f = 1
           else
                 ok_near_equal_f = 0
           endif
           end
Input File: omh/getstarted/near_equal_f.f