# Thread: How to write a natural logarithm in the formula?

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## How to write a natural logarithm in the formula?

when I search in the Help, just get the log().

so what is for the "natural logarithm"?

thanks very much!!!

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## Re: How to write a natural logarithm in the formula?

Which version are you using?

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## Re: How to write a natural logarithm in the formula?

Logs were added to R2015...... a much ballyhooed new feature that I wondered about. Can you tell us why you need logs for?

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## Re: How to write a natural logarithm in the formula?

now I got 2014

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## Re: How to write a natural logarithm in the formula?

I have no idea to make a use for this function, just want to know if it's there and how to spell it.

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## Re: How to write a natural logarithm in the formula?

That's why i asked because there was no log before 2015
So if you type log(1) you will get 1. It is using the e (natural value)

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## Re: How to write a natural logarithm in the formula?

Not being a math PhD, the only use I ever found for logs was to convert a multiplication into an addition. Adding the log of two numbers is the same as multiplying the two numbers. Remember that a log is an exponent. The base 10 log of 100 is 2. The people at Autodesk must know some use for logs. Why else would they include it?

After thinking about it, I bet those algorithmic designs that are on all the magazine covers have a use for logs. Must reread D'Arcy Thompson before I die.

Slide rules (remember those things?) are based on logarithms.

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## Re: How to write a natural logarithm in the formula?

the formula "log(10)" I get a "10" in the revit 2014, and what's it in the revit 2015?

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## Re: How to write a natural logarithm in the formula?

This should help understand

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## Re: How to write a natural logarithm in the formula?

Originally Posted by eabimgxg678896
when I search in the Help, just get the log().

so what is for the "natural logarithm"?

thanks very much!!!
The log(value) function uses base 10. This function is available in Revit 2014 and, I suspect, earlier versions as well.

The ln(value) function (natural logarithm) uses base "e" (approximately 2.718282). This was apparently added in Revit 2015.

As to when you might need to use it in Revit, I have no clue. Natural logarithms are important in mathematics and certain scientific disciplines, particularly when the unknown (variable) is in an exponent. The derivative of the natural logarithm is 1/x. The logarithm of the number 1 using any base is always 0, but only for the natural logarithm is the slope at (1,0) also 1. The base "e" also shows up in compound interest calculations. All other things being equal, as you increase the number of compounding periods per year, the compounding factor approaches a limit of "e" (continuous compounding). As to how any of that applies to architecture.... Keep in mind I think walls should be straight and meet at right angles. Those into "blobitecture" may find a use for logarithms in their calculations.

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