F90_function

Outline of this page

Some Intrinsic functions in Fortran 95, 2003, 2008 are shown in this page.
Functions introduced in this page are chosen based on webmaster's liking.
Explanation of functions are made following gfortran manual.

Some functions in Fortran 95, 2003, 2008

CPU_TIME : CPU elapsed time in seconds (Fortran 95)

Description:

Returns a REAL value representing the elapsed CPU time in seconds.
This is useful for testing segments of code to determine execution time.
If a time source is available, time will be reported with microsecond resolution.
If no time source is available, TIME is set to -1.0.
Note that TIME may contain a, system dependent, arbitrary offset and may not start with 0.0.
For CPU_TIME, the absolute value is meaningless, only differences between subsequent calls to this subroutine, as shown in the example below, should be used.

Class:

Subroutine

Syntax:

CALL CPU_TIME(TIME)

Arguments:

TIME : The type shall be REAL with INTENT(OUT).

Return value:

None

Example:

program test_cpu_time
real :: start, finish
call cpu_time(start)
! put code to test here
call cpu_time(finish)
print '("Time = ",f6.3," seconds.")',finish-start
end program test_cpu_time

COMMAND_ARGUMENT_COUNT : Get number of command line arguments (Fortran 2003)

Description:

COMMAND_ARGUMENT_COUNT returns the number of arguments passed on the command line when the containing program was invoked.

Class:

Inquiry function

Syntax:

RESULT = COMMAND_ARGUMENT_COUNT()

Arguments:

None

Return value:

The return value is an INTEGER of default kind.

Example:

program test_command_argument_count
integer :: count
count = command_argument_count()
print *, count
end program test_command_argument_count

GET_COMMAND_ARGUMENT : Get command line arguments (Fortran 2003)

Description:

Retrieve the NUMBER-th argument that was passed on the command line when the containing program was invoked.

Class:

Subroutine

Syntax:

CALL GET_COMMAND_ARGUMENT(NUMBER [, VALUE, LENGTH, STATUS])

Arguments:

NUMBER : Shall be a scalar of type INTEGER and of default kind, NUMBER >= 0
VALUE : (Optional) Shall be a scalar of type CHARACTER and of default kind.
LENGTH : (Optional) Shall be a scalar of type INTEGER and of default kind.
STATUS : (Optional) Shall be a scalar of type INTEGER and of default kind.

Return value:

After GET_COMMAND_ARGUMENT returns, the VALUE argument holds the NUMBER-th command line argument.
If VALUE can not hold the argument, it is truncated to fit the length of VALUE.
If there are less than NUMBER arguments specified at the command line, VALUE will be filled with blanks.
If NUMBER = 0, VALUE is set to the name of the program (on systems that support this feature).
The LENGTH argument contains the length of the NUMBER-th command line argument.
If the argument retrieval fails, STATUS is a positive number; if VALUE contains a truncated command line argument, STATUS is -1; and otherwise the STATUS is zero.

Example:

PROGRAM test_get_command_argument
INTEGER :: i
CHARACTER(len=32) :: arg
i = 0
DO
CALL get_command_argument(i, arg)
IF (LEN_TRIM(arg) == 0) EXIT
WRITE (*,*) TRIM(arg)
i = i+1
END DO
END PROGRAM

EXECUTE_COMMAND_LINE : Execute a shell command (Fortran 2008)

Description:

EXECUTE_COMMAND_LINE runs a shell command, synchronously or asynchronously.
The COMMAND argument is passed to the shell and executed, using the C library's system call. (The shell is sh on Unix systems, and cmd.exe on Windows.)
If WAIT is present and has the value false, the execution of the command is asynchronous if the system supports it; otherwise, the command is executed synchronously.
The three last arguments allow the user to get status information.
After synchronous execution, EXITSTAT contains the integer exit code of the command, as returned by system.
CMDSTAT is set to zero if the command line was executed (whatever its exit status was).
CMDMSG is assigned an error message if an error has occurred.
Note that the system function need not be thread-safe.
It is the responsibility of the user to ensure that system is not called concurrently.

Class:

Subroutine

Syntax:

CALL EXECUTE_COMMAND_LINE(COMMAND [, WAIT, EXITSTAT, CMDSTAT,CMDMSG ])

Arguments:

COMMAND : Shall be a default CHARACTER scalar.
WAIT : (Optional) Shall be a default LOGICAL scalar.
EXITSTAT : (Optional) Shall be an INTEGER of the default kind.
CMDSTAT : (Optional) Shall be an INTEGER of the default kind.
CMDMSG : (Optional) Shall be an CHARACTER scalar of the default kind.

Example:

program test_exec
integer :: i
call execute_command_line ("external_prog.exe", exitstat=i)
print *, "Exit status of external_prog.exe was ", i
call execute_command_line ("reindex_files.exe", wait=.false.)
print *, "Now reindexing files in the background"
end program test_exec

Note:

Because this intrinsic is implemented in terms of the system function call, its behavior with respect to signaling is processor dependent.
In particular, on POSIX-compliant systems, the SIGINT and SIGQUIT signals will be ignored, and the SIGCHLD will be blocked.
As such, if the parent process is terminated, the child process might not be terminated alongside.

ACOSH : Inverse hyperbolic cosine function (Fortran 2008)

Description:

ACOSH(X) computes the inverse hyperbolic cosine of X.

Class:

Elemental function

Syntax:

RESULT = ACOSH(X)

Arguments:

X The type shall be REAL or COMPLEX.

Return value:

The return value has the same type and kind as X.
If X is complex, the imaginary part of the result is in radians and lies between 0 <= acosh(x) <= pi.

Example:

PROGRAM test_acosh
REAL(8), DIMENSION(3) :: x = (/ 1.0, 2.0, 3.0 /)
WRITE (*,*) ACOSH(x)
END PROGRAM

ASINH : Inverse hyperbolic sine function (Fortran 2008)

Description:

ASINH(X) computes the inverse hyperbolic sine of X.

Class:

Elemental function

Syntax:

RESULT = ASINH(X)

Arguments:

X The type shall be REAL or COMPLEX.

Return value:

The return value is of the same type and kind as X.
If X is complex, the imaginary part of the result is in radians and lies between -pi/2 <= asinh(x) <=pi/2.

Example:

PROGRAM test_asinh
REAL(8), DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /)
WRITE (*,*) ASINH(x)
END PROGRAM

ATANH : Inverse hyperbolic tangent function (Fortran 2008)

Description:

ATANH(X) computes the inverse hyperbolic tangent of X.

Class:

Elemental function

Syntax:

RESULT = ATANH(X)

Arguments:

X : The type shall be REAL or COMPLEX.

Return value:

The return value has same type and kind as X.
If X is complex, the imaginary part of the result is in radians and lies between -pi/2 <= atanh(x) <=pi/2.

Example:

PROGRAM test_atanh
REAL, DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /)
WRITE (*,*) ATANH(x)
END PROGRAM

BESSEL_J0 : Bessel function of the first kind of order 0 (Fortran 2008)

Description:

BESSEL_J0(X) computes the Bessel function of the first kind of order 0 of X.

Class:

Elemental function

Syntax:

RESULT = BESSEL_J0(X)

Arguments:

X : The type shall be REAL, and it shall be scalar.

Return value:

The return value is of type REAL and lies in the range -0.4027... <= Bessel(0, x) <= 1. It has the same kind as X.

Example:

program test_besj0
real(8) :: x = 0.0_8
x = bessel_j0(x)
end program test_besj0

BESSEL_J1 : Bessel function of the first kind of order 1 (Fortran 2008)

Description:

BESSEL_J1(X) computes the Bessel function of the first kind of order 1 of X.

Class:

Elemental function

Syntax:

RESULT = BESSEL_J1(X)

Arguments:

X : The type shall be REAL, and it shall be scalar.

Return value:

The return value is of type REAL and it lies in the range -0.5818... <= Bessel(0, x) <= 0.5818. It has the same kind as X.

Example:

program test_besj1
real(8) :: x = 1.0_8
x = bessel_j1(x)
end program test_besj1

BESSEL_JN : Bessel function of the first kind (Fortran 2008)

Description:

BESSEL_JN(N, X) computes the Bessel function of the first kind of order N of X.
If N and X are arrays, their ranks and shapes shall conform.
BESSEL_JN(N1, N2, X) returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Class:

Elemental function, except for the transformational function BESSEL_JN(N1,N2, X)

Syntax:

RESULT = BESSEL_JN(N, X)
RESULT = BESSEL_JN(N1, N2, X)

Arguments:

N : Shall be a scalar or an array of type INTEGER.
N1 : Shall be a non-negative scalar of type INTEGER.
N2 : Shall be a non-negative scalar of type INTEGER.
X : Shall be a scalar or an array of type REAL; for BESSEL_JN(N1,N2, X) it shall be scalar.

Return value:

The return value is a scalar of type REAL. It has the same kind as X.

Note: The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.

Example:

program test_besjn
real(8) :: x = 1.0_8
x = bessel_jn(5,x)
end program test_besjn

BESSEL_Y0 : Bessel function of the second kind of order 0 (Fortran 2008)

Description:

BESSEL_Y0(X) computes the Bessel function of the second kind of order 0 of X.

Class:

Elemental function

Syntax:

 RESULT = BESSEL_Y0(X)

Arguments:

X The type shall be REAL, and it shall be scalar.

Return value:

The return value is a scalar of type REAL. It has the same kind as X.

Example:

program test_besy0
real(8) :: x = 0.0_8
x = bessel_y0(x)
end program test_besy0

BESSEL_Y1 : Bessel function of the second kind of order 1 (Fortran 2008)

Description:

BESSEL_Y1(X) computes the Bessel function of the second kind of order 1 of X.

Class:

Elemental function

Syntax:

 RESULT = BESSEL_Y1(X)

Arguments:

X The type shall be REAL, and it shall be scalar.

Return value:

The return value is a scalar of type REAL. It has the same kind as X.

Example:

program test_besy1
real(8) :: x = 1.0_8
x = bessel_y1(x)
end program test_besy1

BESSEL_YN : Bessel function of the second kind (Fortran 2008)

Description:

BESSEL_YN(N, X) computes the Bessel function of the second kind of order N of X.
If N and X are arrays, their ranks and shapes shall conform.
BESSEL_YN(N1, N2, X) returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Class:

Elemental function, except for the transformational function BESSEL_YN(N1,N2, X)

Syntax:

RESULT = BESSEL_YN(N, X)
RESULT = BESSEL_YN(N1, N2, X)

Arguments:

N : Shall be a scalar or an array of type INTEGER .
N1 : Shall be a non-negative scalar of type INTEGER.
N2 : Shall be a non-negative scalar of type INTEGER.
X : Shall be a scalar or an array of type REAL; for BESSEL_YN(N1,N2, X) it shall be scalar.

Return value:

The return value is a scalar of type REAL. It has the same kind as X. Note: The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.

Example:

program test_besyn
real(8) :: x = 1.0_8
x = bessel_yn(5,x)
end program test_besyn

GAMMA : Gamma function (Fortran 2008)

Description:

GAMMA(X) computes Gamma (Γ) of X.
For positive, integer values of X the Gamma function simplifies to the factorial function Γ(x) = (x - 1)!.
Γ(x)=∫t^x-1e^-tdt (t=0 → ∞)

Class:

Elemental function

Syntax:

X = GAMMA(X)

Arguments:

X : Shall be of type REAL and neither zero nor a negative integer.

Return value:

The return value is of type REAL of the same kind as X.

Example:

program test_gamma
real :: x = 1.0
x = gamma(x) ! returns 1.0
end program test_gamma

LOG_GAMMA : Logarithm of the Gamma function (Fortran 2008)

Description:

LOG_GAMMA(X) computes the natural logarithm of the absolute value of the Gamma (Γ) function.

Class:

Elemental function

Syntax:

X = LOG_GAMMA(X)

Arguments:

X : Shall be of type REAL and neither zero nor a negative integer.

Return value:

The return value is of type REAL of the same kind as X.

Example:

program test_log_gamma
real :: x = 1.0
x = lgamma(x) ! returns 0.0
end program test_log_gamma