Relational Operators

The following relational operators deliver a logical result:

• .GT. -- greater than.
• .GE. -- greater than or equal to.
• .LE. -- less than or equal to.
• .LT. -- less than.
• .NE. -- not equal to.
• .EQ. -- equal to.

for example,

     i .GT. 12

is an expression delivering a .TRUE. or .FALSE. result.

These above operators are equivalent to the following:

• > -- greater than.
• >= -- greater than or equal to.
• <= -- less than or equal to.
• < -- less than.
• /= -- not equal to.
• = -- equal to.

for example,

     i > 12

Both sets of symbols may be used in a single statement.

Relational operators:

• compare the values of two operands.
• deliver a logical result.
• can be applied to numeric operands (restrictions on COMPLEX which can only use .EQ. and .NE.).
• can be applied to default CHARACTER objects -- both objects are made to be the same length by padding the shorter with blanks. Operators refer to ASCII order (see Appendix 35).
• cannot be applied to LOGICAL objects, for example,

      (bool .NE. .TRUE.)

  is not a valid expression but,

      (.NOT.bool)

  is.
• are used (in scalar) form in IF statements (see Section 8.1) and elementally in the WHERE statement (see Section 11.18).

Consider,

    bool = i.GT.j
    IF (i.EQ.j) c = D
    IF (i == j) c = D

The example demonstrates,

• simple logical assignment using a relational operator,
• IF statements using both forms of relational operators,

When using real-valued expressions (which are approximate) .EQ. and .NE. have no real meaning.

    REAL :: Tol = 0.0001
    IF (ABS(a-b) .LT. Tol) same = .TRUE.

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