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i need to find variable x and the error is " Undefined function or variable 'x'. "

Asked by alireza farrokh on 11 Nov 2017
Latest activity Commented on by alireza farrokh on 11 Nov 2017
>> a=0:2:20; >> y=((1/x)*(exp(-x/a)))+((1/a)*(Ei(-x/a)))==1

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1 Answer

Answer by Mischa Kim
on 11 Nov 2017
 Accepted Answer

A couple of things. In the code you show Ei is not defined and it looks like you need to solve the equation for different a.
Just to get you started: you could use fsolve inside a loop to step through all the different values for a. In the following I picked random values for the parameters to show you how to set up the problem:
a = 1; Ei = 1;
fun = @(x) ((1/x)*(exp(-x/a)))+((1/a)*(Ei*(-x/a))) - 1;
x0 = 1;
xs = fsolve(fun,x0);
fun(xs)

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"Ei=int((exp(t))/t,-x/a,inf);" and "a" should be these numbers:0 2 4 6 8 10 12 14 16 18 20

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