Thread: C math log() function misbehaves...

Originally Posted by matsp

Excel does have two log function, the LOG() function would, in C++ style be defined as:

Code:

double log(double x, double base = 10);

The log10() is shorthand for Log(x, 10).

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Mats

Think you didn't get me well.. Do you mind testing both Excel LOG(7.9454E-18) & LOG10(7.9454E-18) and see if you get different results? That's where my problem is, i get same results...

Originally Posted by matsp

If I do, I suspect that means that I should send a bug report to Microsoft (unless the difference is in the 11th decimal point or so).

What I was trying to say is that log(x) == log10(x) in excel, but it also allows two parameters to log, e.g. log(8, 2), which would give you log2(8) [which is three]. So if you give only one parameter, you get log10, if you give two parameters, log(x, y) you get logy(x).

Does that make more sense?

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Mats

Oh! eish... it's friday so forgive me..

Thnx

Originally Posted by matsp

If I do, I suspect that means that I should send a bug report to Microsoft (unless the difference is in the 11th decimal point or so).

What I was trying to say is that log(x) == log10(x) in excel, but it also allows two parameters to log, e.g. log(8, 2), which would give you log2(8) [which is three]. So if you give only one parameter, you get log10, if you give two parameters, log(x, y) you get logy(x).

Does that make more sense?

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Mats

Interesting this

The Log base 10....

In C/C++: log10(x)... Excel: LOG10(x) == LOG(x) == LOG(x, 10),... Sci Calc: log

Log base e....

In C/C++: log(x) ... Excel: LN(x)... Sci Calc: ln

Can be confusing if using all to test a function...