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Calculate Natural Logarithm in C++: Using math.h Library and Function Names

MARIO159 28138 8
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  • #1 1944165
    MARIO159
    Level 12  
    Posts: 61
    Help: 1
    Questions as in the topic how can I calculate the natural lagarithm from some number. I didn't notice the function in math.h. and what is the name of the function :)
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  • #2 1944301
    Sam Sung
    Level 33  
    Posts: 2014
    Help: 227
    Rate: 583
    There is a function in
    called log :)
    Quote:
    EXP(3) Linux Developer's Manual EXP(3)
    (...)
    SYNTAX
    #include
    (...)
    double log(double x);
    (...)
    DESCRIPTION
    (...)
    The log() function returns the natural logarithm of x.
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  • #3 1944306
    tsoltys
    Level 15  
    Posts: 82
    Help: 12
    Rate: 4
    MARIO159 wrote:
    Questions as in the topic how can I calculate the natural lagarithm of some number. I didn't notice the function in math.h. and what is the name of the function :)


    It is - you just need to look at the math.h documentation.

    Quote:
    NAME
    log - natural logarithm function
    SYNOPSIS
    #include
    double log(double x);
    DESCRIPTION
    The log() function computes the natural logarithm of x, loge(x). The value of x must be positive.
  • #4 4871030
    johnyu
    Level 1  
    Posts: 1
    And is there a logarithm function with two parameters in cmath or math.h (I don't know if they are different)? (logarithm number and base)
  • #5 4871076
    krzychoocpp
    VIP Meritorious for electroda.pl  
    Posts: 1866
    Help: 387
    Rate: 58
    As far as I know, there isn't. Because there is no need.

    $$\frac{\log_c b}{\log_c a} = \log_a b$$
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  • #6 5808376
    marekkiek
    Level 14  
    Posts: 141
    Help: 4
    Rate: 2
    I have this problem in one expression I need to calculate log base 2, but I can't use the logarithm function, I have to write it myself. Is it possible to see the code of a library function and to write something based on its syntax?

    Regards
  • #7 5808490
    Dr.Vee
    VIP Meritorious for electroda.pl  
    Posts: 1784
    Help: 307
    Rate: 76
    You didn't say what numbers you mean (floating point, fixed point). Should the result be rounded or not?

    I wouldn't look at library function code because it's usually too much optimized to read ;)

    Instead, read e.g. on wikipedia http://en.wikipedia.org/wiki/Logarithm#Series_for_calculating_the_natural_logarithm

    Regards,
    Dr. Vee
  • #8 5809845
    Sam Sung
    Level 33  
    Posts: 2014
    Help: 227
    Rate: 583
    Maybe it's something like this - it's not a single expression, but a statement:
    Code: text Expand Select all Copy to clipboard
    for (wynik = 0; x > 1; wynik++, x >>= 1)
  ;
    (ix result of type unsigned int.)
    In a single expression of the C language in the literal sense, it probably can't be done.
    Suspecting a library function is unlikely to help, because it meets other requirements.
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Topic summary

✨ The discussion centers around calculating the natural logarithm in C++ using the math.h library. The primary function for this purpose is identified as "log". Users inquire about the existence of a logarithm function with two parameters for different bases, but it is clarified that such a function is not necessary. One user expresses a need to implement a logarithm base 2 function manually and seeks guidance on writing the code. Suggestions include consulting external resources like Wikipedia for logarithm series and a specific site for integer logarithm calculations. The conversation emphasizes the importance of understanding the types of numbers involved and the potential complexity of library function implementations.
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