mirror of
https://github.com/QB64Official/qb64.git
synced 2024-09-28 11:17:47 +00:00
47 lines
1.7 KiB
Markdown
47 lines
1.7 KiB
Markdown
The [LOG](LOG) math function returns the natural logarithm of a specified numerical value.
|
|
|
|
## Syntax
|
|
|
|
> logarithm! = [LOG](LOG)(value)
|
|
|
|
## Description
|
|
|
|
* value MUST be greater than 0. [ERROR Codes](ERROR-Codes) occurs if negative or zero values are used.
|
|
* The natural logarithm is the logarithm to the base **e = 2.718282** (approximately).
|
|
* The natural logarithm of *a* is defined as the integral from 1 to *a* of dx/x.
|
|
* Returns are default [SINGLE](SINGLE) precision unless the value parameter uses [DOUBLE](DOUBLE) precision.
|
|
|
|
## Example(s)
|
|
|
|
[FUNCTION](FUNCTION) to find the base ten logarithm of a numerical value.
|
|
|
|
```vb
|
|
|
|
FUNCTION Log10#(value AS DOUBLE) STATIC
|
|
Log10# = LOG(value) / LOG(10.#)
|
|
END FUNCTION
|
|
|
|
```
|
|
|
|
> *Explanation:* The natural logarithm of the value is divided by the base 10 logarithm. The LOG of ten is designated as a DOUBLE precision return by using # after the Log10 value. The return tells you the number of times 10 goes into a value.
|
|
|
|
A binary FUNCTION to convert [INTEGER](INTEGER) values using LOG to find the number of digits the return will be.
|
|
|
|
```vb
|
|
|
|
FUNCTION BIN$ (n&)
|
|
IF n& < 0 THEN EXIT FUNCTION 'positive numbers only! negative error!
|
|
FOR p% = 0 TO INT(LOG(n& + .1) / LOG(2)) ' added +.1 to get 0 to work
|
|
IF n& AND 2 ^ p% THEN s$ = "1" + s$ ELSE s$ = "0" + s$ 'find bits on
|
|
NEXT p%
|
|
IF s$ = "" THEN BIN$ = "&B0" ELSE BIN$ = "&B" + s$ 'check for zero return
|
|
END FUNCTION
|
|
|
|
|
|
```
|
|
|
|
> *Explanation:* The LOG of a **positive** [INTEGER](INTEGER) value is divided by the LOG of 2 to determine the number of binary digits that will be returned. The FOR loop compares the value with the exponents of two and determines if a bit is ON or OFF as "1" or "0".
|
|
|
|
## See Also
|
|
|
|
*[EXP](EXP), [&B](&B) (binary number)
|