How can I calculate ln(x) in matlab code?

I am trying to find the syntax for ln(x) in matlab but nothing works. Anyone has an idea?

[Hadi Mohammadi]

for finding ln(x) you can use

log(x)/log(exp(1))

[Rik]

Comment posted as flag by Nicolas Seemann-Ricard:

Wrong, log(x) computes ln(x). In the answer it is assumed log stands for log10

[Rik]

You can calculate a log for any base with log(x)/log(base). Since log calculates the natural logarithm, log(exp(1)) is 1. So the comment is correct, it is just needlessly convoluted.

%this will also compute the natural log, may cause rounding errors on the order of eps(x)
log10(x)/log10(exp(1))

[Baqer Alhabeeb]

The syntax of ln(x) in Matlab is log(x)

[gunaseakar]

thank you

[gunaseakar]

in matlab log is not giving log(x) value ,it is giving ln (x) value

[Steven Lord]

Correct, the log function computes the natural logarithm. If you want the common logarithm (base 10) use log10. If you want the base 2 logarithm use log2.

[Walter Roberson]

@gunaseakar

When you say "in matlab log is not giving log(x)", then what is the mathematical definition of "log(x)" that it might otherwise be returning ?

[Daniel Joseph]

@Walter Roberson

The usual notation from most mathematics textbooks is that log(x) returns values of log of base10, while ln(x) returns natural logarithm. I believe the same convention is followed on regular and scientific calculators. Matlab does it slightly differently, which can catch out users hoping to use log() and ln() convention.

I can understand from @gunaseaker point of view, log(x) should return log base 10 values and not base n. Steven Lord's @Steven Lord answer should have cleared the confusion, with the matlab convention defined.

[Rik]

I haven't done a thorough survey, but I would guesstimate that it is fairly common to see log used in mathematical computing as the natural log. To avoid this confusion, perhaps Matlab should not have a function called log at all, forcing you to specify the base.

While my high school taught log as base 10, my teacher did point out to us that many people would pronounce ln as log. Since powers of e tend to be very common (more so than 10, outside of orders of magnitude), this choice does have some merit.

[Tamba Siama KOMANO]

for me , is yes

Answer 1

[Azzi Abdelmalek]

log(x)

Answer 2

[Walter Roberson]

There seems to be some conception that "ln" is the "right" way to take natural logarithm, and that MATLAB is... deficient... because it uses log() instead.

I researched a number of different programming languges, and found only two so far (Ktolin and Rust) in which natural log was unequivically ln() and log() was incorrect for natural log. A third language, Maple accepts both ln() and log() for natural log. A few additional languages do not offer natural log, including two in which log() is log base 10.

I did not, in my research, find even one language in which natural log is ln() and log base 10 is log()

Languages that use log() for natural log and do not support ln() for natural log

• Ada : Ada.Numerics.Generic_Elementary_Functions defines Log with one parameter is natural logarithm; if second parameter is given then that is the base. https://www.adaic.com/resources/add_content/standards/95lrm/ARM_HTML/RM-A-5-1.html
• C : log() is natural log, log10() is base 10.
• C++ : log() is natural log, log10() is base 10.
• C# : Math.Log with one parameter is natural log, Math.Log with two parameters uses second parameter as base
• Common Lisp : log() with a single parameter is natural logarithm, log() with two parameters uses second parameters as base
• fortran : LOG is natural log, LOG10 is base 10
• Go : math.Log is natural logarithm, math.Logb is logarithm base 2, math.Log10 is logarithm base 10
• java : java.lang.Math.log() is natural logarithm, no other log functions, no two-parameter log
• javascript : Math.log() is natural logarithm; Math.log10() is base 10. Math.log1p() is natural log of 1 more than the input
• Lua : math.log is natural log, no other log functions, no two-parameter log
• Mathematica : Log[] with one parameter is natural logarithm, Log[] with two parameters uses second parameter as base
• MATLAB: log() is natural log, log2() is base 2, log10() is base 10, log1p() is natural log of 1 + x
• php : log() with one parameter is natural log, log() with two parameters uses second parameter as base
• python : math.log() with one parameter is natural log, math.log() with two parameters uses second parameter as base, math.log2() is base 2, math.log10() is base 10, math.log1p() is natural log of 1 + x
• R : log() with one parameter is natural log, log() with two parameters uses second parameter as base, log2() is base 2, log10() is base 10, log1p() is natural log of 1 + x, logb is base 2 . Some of these are wrappers; not all are available in all editions of R; https://www.rdocumentation.org/packages/base/versions/3.6.2/topics/log
• Ruby : Math.log with one parameter is natural log, Math.log with two parameters uses second parameter as base, Math.log2() is base 2, Math.log10 is base 10
• Swift : log() is natural log, log2() is base 2, log10() is base 10, log1p is natural log of 1+x
• typescript : Math.log() is the natural logarithm, no other log functions, no two-parameter log

Languages which do things differently

• Algol : LOG calculates log base 10
• HCL : log() with one parameter is base 10, log() with two parameters is to the given base https://leap.hcldoc.com/help/topic/SSS28S_8.2.1/XFDL_Specification/i_xfdl_g_functions_log.html
• Kotlin : ln() is natural log, log10() is base 10, log2() is base2, log() is log to given base
• Maple: ln() is natural log, log2() is base 2, log10 is base 10, log(x) is also natural logarithm, log(x,b) is base b, log[b](x) is base b
• Pascal : log2() is base 2, log10() is base 10, lnxp1() is natural log of x + 1, log() is log to given base
• Rust : ln() is natural log, log2() is base 2, log10() is base 10, ln_1p() is natural log of x+1, log() is log to given base
• Makefile -- does not support logarithm
• Shell -- csh, ksh, sh, zsh do not support logarithms

Answer 3

[MASIA]

• log(x) → υπολογίζει ln(x) (φυσικός λογάριθμος, βάση e)
• log10(x) → υπολογίζει λογάριθμο με βάση 10
• log2(x) → λογάριθμος με βάση 2

[Rik]

Why did you post your answer in Greek? It looks like a valid answer, but only people who can read Greek will benefit. You might consider translating your answer to English to make sure more people understand your post.

[Walter Roberson]

@Rik

The rule is that people may always post in the language that they feel most comfortable with.

People who cannot happen to read that language are free to ignore the content, or run it through their favorite machine translator.

[DGM]

log(x) → calculates ln(x) (natural logarithm, base e)

log10(x) → calculate logarithm on base 10

log2(x) → logarithm on base 2

If I'm earnestly trying to communicate in a foreign-language (to me) forum, I prefer to post in my own native language and provide a machine translation. That way I maximize accessibility, while hopefully providing enough redundancy to account for any translation errors to which I might be blind. That said, I admit I'm not always so motivated. :)

[Rik]

Just to clarify: I didn't mean to suggest MASIA was doing anything wrong. I was merely pointing to the presumed difference in users on this forum who are able to read Greek vs English. It wouldn't surprise me if all Greeks visiting this page would be able to read English, while the reverse is definitely not the case.

@DGM That's a very good strategy (although I must admit I'm too lazy to do that for English and too stubborn to do that for French and Spanish).