MATLAB Function Reference |

Modified Bessel function of the first kind

**Syntax**

**Definitions**

where is a real constant, is called the *modified Bessel's equation*, and its solutions are known as *modified Bessel functions*.

and form a fundamental set of solutions of the modified Bessel's equation for noninteger . is defined by

is a second solution, independent of . It can be computed using `besselk`

.

**Description**

```
I = besseli(nu,Z)
```

computes the modified Bessel function of the first kind, , for each element of the array `Z`

. The order `nu`

need not be an integer, but must be real. The argument `Z`

can be complex. The result is real where `Z`

is positive.

If `nu`

and `Z`

are arrays of the same size, the result is also that size. If either input is a scalar, it is expanded to the other input's size. If one input is a row vector and the other is a column vector, the result is a two-dimensional table of function values.

```
I = besseli(nu,Z,1)
```

computes `besseli(nu,Z).*exp(-abs(real(Z)))`

.

```
[I,ierr] = besseli(...)
```

also returns completion flags in an array the same size as `I`

.

**Examples**

format long z = (0:0.2:1)'; besseli(1,z) ans = 0 0.10050083402813 0.20402675573357 0.31370402560492 0.43286480262064 0.56515910399249

**Example 2.** `besseli(3:9,(0:.2,10)',1)`

generates the entire table on page 423 of [1] Abramowitz and Stegun, *Handbook of Mathematical Functions*.

**Algorithm**

The `besseli`

functions uses a Fortran MEX-file to call a library developed by D. E. Amos [3] [4].

**See Also**

`airy`

, `besselh`

, `besselj`

, `besselk`

, `bessely`

**References**

[1] Abramowitz, M. and I.A. Stegun, *Handbook of Mathematical Functions*,
National Bureau of Standards, Applied Math. Series #55, Dover Publications,
1965, sections 9.1.1, 9.1.89 and 9.12, formulas 9.1.10 and 9.2.5.

[2] Carrier, Krook, and Pearson, *Functions of a Complex Variable: Theory and
Technique*, Hod Books, 1983, section 5.5.

[3] Amos, D. E., "A Subroutine Package for Bessel Functions of a Complex
Argument and Nonnegative Order," *Sandia National Laboratory Report*,
SAND85-1018, May, 1985.

[4] Amos, D. E., "A Portable Package for Bessel Functions of a Complex
Argument and Nonnegative Order," *Trans. Math. Software*, 1986.

besselh | besselj |