Hi all,I want to use matlab to calculate the exponential integral,I know that the official function ExpIntegralE in Mathematica can calculate it.

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ma Jack 2022-8-30

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评论： ma Jack 2022-9-7

采纳的回答： Paul

As shown in the title, I want to find a relatively authoritative code to calculate exponential integral

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Answer 1

Paul 2022-8-31

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ExpIntegralE in Mathematica seems to be the same as the two-argument form of expint in the Symbolic Math Toolbox.

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Paul 2022-9-4

在 MATLAB Online 中打开

"there is no official matlab function that is used like expint(n,x), in matlab "

Using the function at the doc page for expint linked above in this Answer

expint(sym(3),sym(5.5))

ans =

Get the decimal representation

vpa(expint(sym(3),sym(5.5)))
ans = 0.00049877076767550924005965009248623

which is the same result using ExpIntegalE in Mathematica link

ma Jack 2022-9-7

Sorry guys, you're right, forgive my carelessness

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Answer 2

John D'Errico 2022-8-30

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编辑：John D'Errico 2022-8-30

在 MATLAB Online 中打开

Is there a reason why you would not just use expint?

help expint
 EXPINT Exponential integral function.
    Y = EXPINT(X) is the exponential integral function for each
    element of X.  The exponential integral is defined as:
 
    EXPINT(x) = integral from x to Inf of (exp(-t)/t) dt, for x > 0.
    
    By analytic continuation, EXPINT is a scalar-valued function in
    the complex plane cut along the negative real axis.
 
    Another common definition of the exponential integral function is
    the Cauchy principal value integral from -Inf to X of (exp(t)/t)
    dt, for positive X.  This is denoted as Ei(x). The relationships
    between EXPINT(x) and Ei(x) are as follows:
 
        EXPINT(-x+i*0) = -Ei(x) - i*pi, for real x > 0
        Ei(x) = REAL(-EXPINT(-x)), for real x > 0
 
    Class support for input X:
       float: double, single

    Documentation for expint
       doc expint

    Other functions named expint

       codistributed/expint    gpuArray/expint    sym/expint

Probably you did not look for it. And that was what you did wrong. When you don't know how to do something in MATLAB, LEARN TO USE LOOKFOR. In my case, this identified many possible things, but do you see the 6th item on the list?

lookfor exponential
expmdemo1                      - Matrix exponential via Pade approximation.
expmdemo2                      - Matrix exponential via Taylor series.
expmdemo3                      - Matrix exponential via eigenvalues and eigenvectors.
exp                            - Exponential.
expm                           - Matrix exponential.
expint                         - Exponential integral function.
...

Any guesses what expint would do? The point is, USE LOOKFOR.

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ma Jack 2022-9-4

In fact, there is no official matlab function that is used like expint(n,x), in matlab it can only be expint(x), which is equivalent to ExpIntegralE[1, x] in mathematica, but what I want is ExpIntegralE[n, x]