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Solving equations involving log

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Masood Abbasi
Masood Abbasi 2018-11-17
回答： Star Strider 2018-11-17
Hi, All
How can i solve for 'x' in following equation given values of 'N' , 'U' and 'r' using Matlab.
matlab_eqn.png

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回答（3 个）

Rick Rosson
Rick Rosson 2018-11-17
编辑：Rick Rosson 2018-11-17
x = log ( 1 + U * (r^N - 1) ) / log(r);
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Masood Abbasi
Masood Abbasi 2018-11-17
Thanks Rick
I know that its the equation we get, but how can i formulate my equation in Matlab equation solver to get solution (x) without writing all equation myself

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madhan ravi
madhan ravi 2018-11-17
编辑：madhan ravi 2018-11-17
syms x r N U
eqn=(r^x-1)/(r^N-1)==U;
x=solve(eqn,x);
pretty(x) %to display in a neat manner
Star Strider
Star Strider 2018-11-17
Using built-in MATLAB functions (no Toolboxes required):
U = 4.2;
N = 1.1;
r = 3.1;
fcn = @(x) ((r.^x - 1)./(r.^N -1)) - U;
x_soln = fzero(fcn, 1)
and more robustly, using the Optimization Toolbox:
x_soln = fsolve(fcn, 1)
Experiment to get the result you want.

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