# Calculating In(a)

Discussion in 'Math' started by sairfan1, Mar 2, 2013.

1. ### sairfan1 Thread Starter Active Member

May 24, 2012
46
1
hi,

i'm not very good in math, while solving some equation for an electronic project, i had In(R) where R is resistance, i want to know what is called this"In" in maths, how do we calculate this on paper.

2. ### WBahn Moderator

Mar 31, 2012
23,093
6,946
You need to provide more information. I have no idea what "In" is refering to. Are you sure it isn't "ln" (lower case L)? If so, then that is the natural logarithm function. But that doesn't get you out of the woods because R has units and the argument to the natural log function, like the arguments to all trascendental functions, must be dimensionless.

3. ### sairfan1 Thread Starter Active Member

May 24, 2012
46
1
thanks for help, i attached image file showing formula, i guess you are right, its related to logarithm.

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4. ### t06afre AAC Fanatic!

May 11, 2009
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Most scientific calculators do have the ln function. Included the windows calculator then in scientific mode

5. ### sairfan1 Thread Starter Active Member

May 24, 2012
46
1
what is this "In" function called(full form), so that i could search to learn more about it,

thanks.

May 11, 2009
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7. ### WBahn Moderator

Mar 31, 2012
23,093
6,946
Since you've established that it is "ln", you need to STOP using "In". It is NOT "In".

As for what it is called, re-read my first response:

The formula you posted is fundamentally flawed because, as I stated before, R has units and the argument to the natural log function, like the arguments to all trascendental functions, must be dimensionless.

At the very least, whoever came up with that formula is being unforgivably sloppy.

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8. ### sairfan1 Thread Starter Active Member

May 24, 2012
46
1
thanks, in fact i got confused, because on scientific calculator there is key "log" for logarithm and there is also key "ln" or may be "In", that's why i thought may be its related to that.

9. ### WBahn Moderator

Mar 31, 2012
23,093
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It IS related to that.

ln() is the logarithm to the base e, also known as the natural logarithm.

log() is the logarithm to the base 10, also knows as the common logarithm.

The definition of a logarithm (well, one definition, there are many) is as follows:

If x = b^y, then y is the base-b logarithm of x. That's all there is to it.

For the ln(), b = e = 2.7182818284590452353602874713527....

For the log(), b = 10

But while this is the most common convention on scientific calculators, many programming language libraries do not follow this convention. Some use log() for the natural log and log10() for the common log. Mathematicians, in particular, like to use log() for the natural log and log_10() (a subscript 10) for the common log (on the rare occasion that they use it).

The bottom line is that you need to gain an understanding for the fundamental concepts at play so that you can place yourself in a position to figure out what is meant in a particular situation instead of relying on memorized "facts" that often aren't as engraved in stone as we would like to believe.

Last edited: Mar 4, 2013
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