The exponential integral (expint) of x is defined as E1, then how E2 is defined ? Can it be solved using MATLAB?

how E2 is defined?

Expression is =

Answer 1

[Torsten]

Why do you ask the same question again ?

It has been answered here:

https://de.mathworks.com/matlabcentral/answers/1665879-how-can-i-write-e2-in-matlab-is-it-expint?s_tid=srchtitle

But you can also call it directly from MATLAB using

s = expint(x,2)

https://de.mathworks.com/help/symbolic/expint.html

And the definition of E_n is here under the point "Generalization":

https://en.wikipedia.org/wiki/Exponential_integral

[Dhawal Beohar]

I asked again because I was looking for more explanation, which I can understand better.

But your answer helped me. Thanks !

[Torsten]

But you can also call it directly from MATLAB using

s = expint(x,2)

Sorry, should read

s = expint(2,x)

[Dhawal Beohar]

Yes, I got that. Cheers !

[Dhawal Beohar]

Hi ! i will appreciate your help, I am having an error:

FSOLVE requires all values returned by functions to be of data type double.

function fval = fun(u)

d1=20;

n=10^-11.4;

m=2.7;

a=0.5;

T=1;

PsByN_0dB=25;

PsByN_0=10.^(PsByN_0dB/10);

fun2 = @(u) ((1./u).*log(expint(2,sym(-PsByN_0.*u))).*exp(-PsByN_0*u));

u0 = -0.0031622776;

U = fsolve(fun2,u0)

[Torsten]

Try this script:

x = 3.0;
y = expint(2,x)

Does it work ?

If yes, expint also accepts inputs for x of type double. Then change in your code from above the line

fun2 = @(u) ((1./u).*log(expint(2,sym(-PsByN_0.*u))).*exp(-PsByN_0*u));

to

fun2 = @(u) expint(2,-PsByN_0*u) - 1

since your expression will be 0 if and only if

expint(2,-PsByN_0*u) = 1

Otherwise, use

fun2 = @(u) double(expint(2,sym(-PsByN_0*u))) - 1

[Dhawal Beohar]

Thanks Torsten for all the help !

fun2 = @(u) double(expint(2,sym(-PsByN_0*u))) - 1

This worked !

[Torsten]

So expint does not accept doubles as input, e.g.

x = 3;

y = expint(2,x)

does not work ?

[Dhawal Beohar]

No, it didn't worked.

Error using expint

Too many input arguments.

[Torsten]

I think that's idiotic.

People who work with expint want it to have numerical output with numerical input, I guess.

[Dhawal Beohar]

Yes, I agree with you.