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

>> a=0:2:20; >> y=((1/x)*(exp(-x/a)))+((1/a)*(Ei(-x/a)))==1

Answer 1

[Mischa Kim]

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)

[alireza farrokh]

"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