# DBESJ0, DBESJ1, DBESJN, DBESY0, DBESY1, DBESYN

Portability Functions: Compute the double-precision values of Bessel functions of the first and second kinds.

## Module

USE IFPORT

result = DBESJ0 (value)

result = DBESJ1 (value)

result = DBESJN (n, value)

result = DBESY0 (posvalue)

result = DBESY1 (posvalue)

result = DBESYN (n, posvalue)

value | (Input) REAL(8). Independent variable for a Bessel function.
n | (Input) INTEGER(4). Specifies the order of the selected Bessel function computation.
posvalue | (Input) REAL(8). Independent variable for a Bessel function. Must be greater than or equal to zero.

## Results

DBESJ0, DBESJ1, and DBESJN return Bessel functions of the first kind, orders 0, 1, and n, respectively, with the independent variable value.

DBESY0, DBESY1, and DBESYN return Bessel functions of the second kind, orders 0, 1, and n, respectively, with the independent variable posvalue.

Negative arguments cause DBESY0, DBESY1, and DBESYN to return a huge negative value.

Bessel functions are explained more fully in most mathematics reference books, such as the Handbook of Mathematical Functions(Abramowitz and Stegun. Washington: U.S. Government Printing Office, 1964). These functions are commonly used in the mathematics of electromagnetic wave theory.

See the descriptions of the BESSEL_* functions, if you need to use quad-precision (REAL(16)).

## Example

        USE IFPORT
        real(8) besnum, besout
    10  read *, besnum
        besout = dbesj0(besnum)
        print *, 'result is ',besout
        goto 10
        end

Parent topic: C to D

## See Also

BESJ0, BESJ1, BESJN, BESY0, BESY1, BESYN