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45 lines
2.1 KiB
Plaintext
45 lines
2.1 KiB
Plaintext
The [[LOG]] math function returns the natural logarithm of a specified numerical value.
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{{PageSyntax}}
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: {{Parameter|logarithm!}} = [[LOG]]({{Parameter|value}})
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{{PageDescription}}
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* {{Parameter|value}} MUST be greater than 0. [[ERROR Codes|"Illegal function call" error]] occurs if negative or zero values are used.
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* The natural logarithm is the logarithm to the base '''e = 2.718282''' (approximately).
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* The natural logarithm of ''a'' is defined as the integral from 1 to ''a'' of dx/x.
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* Returns are default [[SINGLE]] precision unless the value parameter uses [[DOUBLE]] precision.
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{{PageExamples}}
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''Example 1:'' [[FUNCTION]] to find the base ten logarithm of a numerical value.
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{{CodeStart}}
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{{Cl|FUNCTION}} Log10#(value {{Cl|AS}} {{Cl|DOUBLE}}) {{Cl|STATIC}}
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Log10# = {{Cl|LOG}}(value) / LOG(10.#)
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{{Cl|END FUNCTION}} '' ''
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{{CodeEnd}}
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:''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.
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''Example 2:'' A binary FUNCTION to convert [[INTEGER]] values using LOG to find the number of digits the return will be.
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{{CodeStart}} '' ''
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{{Cl|FUNCTION}} BIN$ (n&)
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{{Cl|IF}} n& < 0 {{Cl|THEN}} {{Cl|EXIT FUNCTION}} 'positive numbers only! negative error!
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{{Cl|FOR}} p% = 0 {{Cl|TO}} {{Cl|INT}}({{Cl|LOG}}(n& + .1) / {{Cl|LOG}}(2)) 'added +.1 to get 0 to work
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{{Cl|IF}} n& {{Cl|AND}} 2 ^ p% {{Cl|THEN}} s$ = "1" + s$ {{Cl|ELSE}} s$ = "0" + s$ 'find bits on
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{{Cl|NEXT}} p%
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{{Cl|IF}} s$ = "" {{Cl|THEN}} BIN$ = "&B0" {{Cl|ELSE}} BIN$ = "&B" + s$ 'check for zero return '' ''
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{{Cl|END FUNCTION}}
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{{CodeEnd}}
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: ''Explanation:'' The LOG of a '''positive''' [[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".
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{{PageSeeAlso}}
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*[[EXP]], [[&B]] (binary number)
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{{PageNavigation}}
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