# \$ZLN

Returns the natural logarithm of the specified number.

## Synopsis

```\$ZLN(n)
```

### Parameter

Argument Description
n Any positive nonzero number, which can be specified as a value, a variable, or an expression.

## Description

\$ZLN returns the natural logarithm (base e) value of n.

Specifying zero or a negative number results in an <ILLEGAL VALUE> error.

The corresponding natural logarithm power function is \$ZEXP.

## Examples

The following example writes the natural log of the integers 1 through 10:

```   FOR x=1:1:10 {
WRITE !,"The natural log of ",x," = ",\$ZLN(x)
}
QUIT```

returns:

```The natural log of 1 = 0
The natural log of 2 = .6931471805599453089
The natural log of 3 = 1.098612288668109691
The natural log of 4 = 1.386294361119890618
The natural log of 5 = 1.609437912434100375
The natural log of 6 = 1.791759469228055002
The natural log of 7 = 1.945910149055313306
The natural log of 8 = 2.079441541679835929
The natural log of 9 = 2.197224577336219384
The natural log of 10 = 2.302585092994045684```

The following example shows the relationship between \$ZLN and \$ZEXP:

```   SET x=\$ZEXP(1) ; x = 2.718281828459045236
WRITE \$ZLN(x)```

returns 1.

`   WRITE \$ZLN(0)`

issues an <ILLEGAL VALUE> error.