Intrinsic Functions

FORTRAN provides a variety of intrinsic functions which may be used in any program unit. They are subject neither to type declarations nor IMPLICIT statements. Their names are not reserved keywords but to avoid confusion, it is inadvisable to use these names as arrays, constants, variables or user-defined external subprograms. If, however, it is desirable to use the name of an intrinsic function as the name of a user-defined external subprogram, then the name must be declared in an EXTERNAL statement in the program unit which invokes it.

If an intrinsic function appears in the actual argument list of an external subprogram invocation or CALL statement, then it must be declared in an INTRINSIC statement. 

PROGRAM MAIN
REAL      PI
INTRINSIC COS,SIN
PARAMETER(PI=3.14159265)
WRITE(*,*)'Cosine Function'
CALL TABLE(COS,-PI,PI)
WRITE(*,*)'Sine Function'
CALL TABLE(SIN,-PI,PI)
...
STOP 'End of program'
END

SUBROUTINE TABLE(F,LOWER,UPPER)
REAL    F,LOWER,UPPER,X
...  
WRITE(*,*)X,F(X)
...
RETURN
END

The intrinsic functions COS and SIN are passed to a user-defined SUBROUTINE called TABLE and so must be declared as INTRINSIC in the calling program unit (the main program in this case).

The following table outlines the generic forms of these functions. C stands for CHARACTER data, D for DOUBLE PRECISION, I for INTEGER, L for LOGICAL, R for REAL (single precision) and X for COMPLEX (single precision). Note that the MAX and MIN intrinsic functions may take any number of arguments but the rest take either one or two arguments.

Function Argument Type Return Type Description
ABS X R modulus of a complex number
ABS DIR DIR absolute value of a number
ACOS DR DR arccosine of a number
AIMAG X R imaginary part of a complex number
AINT DR DR truncates fractional part but preserves data type
ANINT DR DR rounds to nearest whole number but preserves data type
ASIN DR DR arcsine of a number
ATAN DR DR arctangent of a number
ATAN2 DR,DR DR arctangent of arg1 divided by arg2 resolved into the correct quadrant
CHAR I C returns nth character in character code table
CMPLX DIRX X converts to the COMPLEX data type
CMPLX DIR,DIR X converts to the COMPLEX data type arg1 + i arg2
CONJG X X complex conjugate of a complex number
COS DRX DRX cosine of an angle in radians
COSH DR DR hyperbolic cosine
DBLE DIRX D converts to the DOUBLE PRECISION data type
DIM DIR,DIR DIR if arg1 > arg2, then returns arg1 - arg2; otherwise 0
DPROD R,R D double precision product of two single precision numbers
EXP DRX DRX exponential
ICHAR C I position of first character in string in the character code table
INDEX C,C I searches first string and returns position of second string within it
INT DIRX I converts to the INTEGER data type by truncation
LEN C I length of character argument
LGE C,C L lexical comparison; true if arg1 >= arg2 in ASCII character code
LGT C,C L lexical comparison; true if arg1 > arg2 in ASCII character code
LLE C,C L lexical comparison; true if arg1 <= arg2 in ASCII character code
LLT C,C L lexical comparison; true if arg1 < arg2 in ASCII character code
LOG DRX DRX natural logarithm
LOG10 DRX DRX common logarithm
MAX DIR,DIR,... DIR maximum value of arguments
MIN DIR,DIR,... DIR minimum value of arguments
MOD DIR,DIR DIR,DIR arg1 modulo arg2
NINT DR I converts to the INTEGER data type by rounding
REAL X R real part of a complex number
REAL DIR R converts to the REAL data type
SIGN DIR,DIR DIR if arg2 < 0, then returns -arg1; else +arg1
SIN DRX DRX sine of an angle in radians
SINH DR DR hyperbolic sine
SQRT DRX DRX square root
TAN DR DR tangent of an angle in radians
TANH DR DR hyperbolic tangent
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