Intrinsic Functions

FORTRAN 77 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 function reference or CALL statement, then its specific name must be declared in an INTRINSIC statement.

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 n^th 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

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 n^th 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

Specific names must be used when intrinsic function names are used as actual arguments in a procedure call. The specific name must be declared in the INTRINSIC statement of the calling program unit. The following generic functions have specific names for different data types.

Generic Name Specific Name

Complex Double Precision Integer Real

ABS CABS DABS IABS ABS

ACOS DACOS ACOS

AINT DINT AINT

ANINT DNINT ANINT

ASIN DASIN ASIN

ATAN DATAN ATAN

ATAN2 DATAN2 ATAN2

COS CCOS DCOS COS

COSH DCOSH COSH

DIM DDIM IDIM DIM

EXP CEXP DEXP EXP

LOG CLOG DLOG ALOG

LOG10 DLOG10 ALOG10

MOD DMOD MOD AMOD

NINT IDNINT NINT

SIGN DSIGN ISIGN SIGN

SIN CSIN DSIN SIN

SINH DSINH SINH

SQRT CSQRT DSQRT SQRT

TAN DTAN TAN

TANH DTANH TANH

Generic Name	Specific Name
Complex	Double Precision	Integer	Real
`ABS`	`CABS`	`DABS`	`IABS`	`ABS`
`ACOS`		`DACOS`		`ACOS`
`AINT`		`DINT`		`AINT`
`ANINT`		`DNINT`		`ANINT`
`ASIN`		`DASIN`		`ASIN`
`ATAN`		`DATAN`		`ATAN`
`ATAN2`		`DATAN2`		`ATAN2`
`COS`	`CCOS`	`DCOS`		`COS`
`COSH`		`DCOSH`		`COSH`
`DIM`		`DDIM`	`IDIM`	`DIM`
`EXP`	`CEXP`	`DEXP`		`EXP`
`LOG`	`CLOG`	`DLOG`		`ALOG`
`LOG10`		`DLOG10`		`ALOG10`
`MOD`		`DMOD`	`MOD`	`AMOD`
`NINT`		`IDNINT`		`NINT`
`SIGN`		`DSIGN`	`ISIGN`	`SIGN`
`SIN`	`CSIN`	`DSIN`		`SIN`
`SINH`		`DSINH`		`SINH`
`SQRT`	`CSQRT`	`DSQRT`		`SQRT`
`TAN`		`DTAN`		`TAN`
`TANH`		`DTANH`		`TANH`