The log function does exactly what you want.
log(14 - y)
If you want a base 10 log, you use log10. There is also a log2 function, which gives a base 2 log. Other bases are achieved using the simple relation
log(X)/log(b)
produces a log to the base b. You could write a function for it as:
logb = @(X,b) log(X)/log(b);
logb(9,3)
ans =
2
which is as expected.
Finally, there is the reallog function, which also does the natural log, but it produces an error when the log would have been a complex number.
log(-2)
ans =
0.693147180559945 + 3.14159265358979i
reallog(-2)
Error using reallog
Reallog produced complex result.
But for the more normal case, reallog does the same thing as log.
log(2)
ans =
0.693147180559945
reallog(2)
ans =
0.693147180559945 Answer from John D'Errico on mathworks.com
MathWorks
mathworks.com › matlabcentral › answers › 1465394-how-do-i-calculate-a-logarithm-of-a-variable-base
How do I calculate a logarithm of a variable base? - MATLAB Answers - MATLAB Central
October 2, 2021 - I saw that calculating log of the base of 10 or e is possible. for an example: after typing log (a,b) - I recieve an ERROR message. I'd like to use "a" as a varying number and change it using a loop until I'll get a good result. "a" can be for an example - 1.05, 1.003.... ... Too many input arguments. ... Sign in to comment. Sign in to answer this question. ... https://www.mathworks.com/matlabcentral/answers/1465394-how-do-i-calculate-a-logarithm-of-a-variable-base#answer_800204
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mathworks.com › matlabcentral › fileexchange › 14866-logb
logb - File Exchange - MATLAB Central
September 1, 2016 - Examples: 1) To calculate the base 5 logarithm of 3: y = logb(3,5) 2) To calculate element-wise the log of a non-scalar input using different bases: y = logb(magic(3),[1 2 3; 4 5 6; 7 8 9]); See also: log, log10, log2 · Brett Shoelson (2025). ...
MATLAB Central
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How to calculate log? - MATLAB Cody - MATLAB Central
There is a log that have base 5. How to calculate? ... Find the treasures in MATLAB Central and discover how the community can help you!
MathWorks
mathworks.com › matlab › mathematics › elementary math
Exponents and Logarithms - MATLAB & Simulink
In addition to common functions like exp and log, MATLAB® has several other related functions to allow flexible numerical calculations. The expm1 and log1p functions compensate for numerical round-off errors in small arguments, while the reallog, realpow, and realsqrt functions restrict the range of these functions to real numbers.
MathWorks
mathworks.com › matlabcentral › answers › 1808600-formula-for-changing-the-base-of-a-logarithm-is-loga-n-logb-n-logb-a-a-use-matlab-s-fu
formula for changing the base of a logarithm is: loga(N) = (logb(N))/(logb(a)) (a) Use MATLAB's function log (x) to cal... - MATLAB Answers - MATLAB Central
September 20, 2022 - formula for changing the base of a logarithm is:... Learn more about matlab, log
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Matlab log | Learn the different examples of Matlab log
March 8, 2023 - log10(5) [Passing 5 as an argument to the log10 method as we need its common logarithm] [Mathematically, the log of 5 to the base “10” is 0.6990] This is how our input and output will look like in the Matlab command window:
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Top answer 1 of 5
17
Consider this example:
%# some random data
x = 2.^(0:10);
y = rand(size(x));
plot(log2(x), y) %# plot on log2 x-scale
set(gca, 'XTickLabel',[]) %# suppress current x-labels
xt = get(gca, 'XTick');
yl = get(gca, 'YLim');
str = cellstr( num2str(xt(:),'2^{%d}') ); %# format x-ticks as 2^{xx}
hTxt = text(xt, yl(ones(size(xt))), str, ... %# create text at same locations
'Interpreter','tex', ... %# specify tex interpreter
'VerticalAlignment','top', ... %# v-align to be underneath
'HorizontalAlignment','center'); %# h-aligh to be centered
2 of 5
15
You can plot directly using the plot command
plot (log2(x), y)
but then your x ticks will be the logarithm rather than the actual value. You could either just change your label
xlabel('Log (base 2) of quantity X');
or you can redo the ticks manually.
xt = get(gca, 'XTick');
set (gca, 'XTickLabel', 2.^xt);
Or you can be really fancy
xticks = 10:25;
set(gca, 'XTick', xticks);
for j = 1:length(xticks)
xtl{j} = ['2^' num2str(xticks(j))];
end
set(gca, 'XTickLabel', xtl)
which will evenly space the tick marks on the log scale, and label them according to their power of 2
Quora
quora.com › How-can-I-implement-log-ln-and-e-in-MATLAB
How to implement log, ln, and e in MATLAB - Quora
MATLAB already provides the standard logarithm functions and the constant e, but if you need to implement them yourself (for learning, custom numeric types, or constrained environments), here are concise, reliable approaches. ... Natural log: log(x) returns ln(x) (base e).
MathWorks
mathworks.com › matlabcentral › answers › 52224-log-of-10-base-b-where-b-is-defined-as-1-to-10-in-increments-of-1
Log of 10 base "b" where 'b' is defined as 1 to 10 in increments of 1 - MATLAB Answers - MATLAB Central
October 29, 2012 - It is for school BTW, and all i know is Log(base'b')(X)=log(base'e')(x) over log(base'b'(b) where be is all values between 1-10. Sign in to comment. Sign in to answer this question. ... https://www.mathworks.com/matlabcentral/answers/52224-log-of-10-base-b-where-b-is-defined-as-1-to-10-in-increments-of-1#answer_63659
MathWorks
mathworks.com › matlab › mathematics › elementary math › exponents and logarithms
log - Natural logarithm - MATLAB
Y = log(X) returns the natural logarithm ln(x) of each element in array X.
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mathworks.com › matlab › mathematics › elementary math › exponents and logarithms
log10 - Common logarithm (base 10) - MATLAB
Examine several values of the base 10 logarithm function. Calculate the common logarithm of 1. ... The result is 0, so this is the x-intercept of the log10 function. Calculate the common logarithm of 10. ... Calculate the common logarithm of 100. ... Calculate the common logarithm of 0. ... Create a vector of numbers in the interval [0.5 5].