Log()

[ThomasJones]

Does anyone know how to calculate the LOG of a number without using the LOG function in VB or on a calculator?

For example, I use Log(num) to get a result but what calculation is performed to do that? If I learned it, I forgot how.

Thanks for any help.

[siyan]

http://www.google.ca/search?q=logarithm+algorithm

[BillyYank42]

Also, Logarithms are inverses of exponential functions. Therefore if E^x=q then logEq=x and can be solved by a "change of base" or logE/logq = x.


Chris

[prog_tom]

Originally posted by BillyYank42
Also, Logarithms are inverses of exponential functions. Therefore if E^x=q then logEq=x and can be solved by a "change of base" or logE/logq = x.


Chris

But you still used Log function.

[BillyYank42]

All I was saying was that if you did (e^x)^-1 that it would be the same as doing a log.


Chris

[Guv]

ThomasJones: There are probably some power series which can be used. A Web Search or a trip to a good library should provide the coefficients. The first post by BillyYank42 could be used, but might be a bit more time consuming than other methods. I am not sure what he meant by his second post: Reciprocal of exponential or inverse of exponential.

As suggested by BillyYank42, solve e^x - Number = 0

When a value is found for the above, x = ln(Number) Id Est: Log_e(Number) = x

You can find a value for x using the Newton method of successive approximations.

Note that e^x is the derivative of F(x) = e^x - Number, which is required when using the Newton method.

[BillyYank42]

inverse of exponential.


Chris

[evexa]

Log (base5) 25
is basically - the power to which 5 is raised to get 25.
which is 2.
You don't want to use a calculator AT ALL?