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I am using Wolfram Mathematica 11. Given these quantities:

v = 3; 
Y = Sqrt[v^2 - X^2];

Ja = BesselJ[0, X]; 
Jap = -BesselJ[1, X];

Ka = BesselK[0, Y]; 
Kap = -BesselK[1, Y];

side1 = Jap / (X*Ja); 
side2 = -Kap / (Y*Ka);

I would like to obtain the same visual output as:

Plot[{side1, side2}, {X, 0, 10}]

but on a .txt file, simply containing a table of values in this notation:

 0.0000000000e+00 -inf -inf
 3.0060120240e-02 -2.3042094212e+00 -2.1217639107e+01
 6.0120240481e-02 -1.8613440179e+00 -1.0654661322e+01

First column should list the X values; second column should list the corresponding side1 values; third column the corresponding side2 values.

How is it possible, with and without adaptive sampling?

Important note: I am not obliged to use Plot. I would like to obtain a .txt output file with the lines in the same format as above. The way it is created (through Plot or any other suitable function) is not important.


Edit: I obtained two separate tables (in the desired format) this way:

pts1 = Cases[Plot[side1[X], {X, 0, 10}, PlotRange -> {-1.6, 1.6}], Line[data_] :> data, All]~Flatten~1; Export["file1.txt",pts1,"Table"]

pts2 = Cases[Plot[side2[X], {X, 0, 10}, PlotRange -> {-1.6, 1.6}], Line[data_] :> data, All]~Flatten~1; Export["file2.txt",pts2,"Table"]

Thanks to @MarcoB for his suggestions in the comments. Each file has only two columns. Note that file1.txt spans from X = 0 to X = 10, while file2.txt from X = 0 to X = 1.778, for the reasons pointed out by @m_golberg.

I was looking for a single table. This solution instead would demand to the external reader, which uses the table, the task to correctly overlap the two tables. This was not my initial intention, but if this is the only way, it is acceptable as well.

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  • $\begingroup$ Your code based on extracting data points from Plot is a good idea to exploit its adaptive sampling. When adapting code, though, it is always a good idea to test it step by step. For instance, if you ran just Plot[side1@X, {X, 0, 10}], you would have realized that it returned an empty plot. Indeed, side is not a function in your code, so it does not make sense to apply it to X. Instead, use Plot[side1, {X, 0, 10}]. Then Cases[Plot[side1, {X, 0, 10}], Line[data_] :> data, All]~Flatten~1 will give you a list of points including all four branches of the side1 function. $\endgroup$
    – MarcoB
    Commented Dec 9, 2019 at 16:52
  • $\begingroup$ @MarcoB I tried as suggested, but I obtained exactly the opposite. Plot[side1@X, {X, 0, 10}] prints the function side1, while Plot[side1, {X, 0, 10}] generates an empty plot. Consequently, Cases[Plot[side1, {X, 0, 10}], Line[data_] :> data, All]~Flatten~1 gives an empty output. $\endgroup$
    – BowPark
    Commented Dec 10, 2019 at 11:50
  • $\begingroup$ @MarcoB Instead, Cases[Plot[side1, {X, 0, 10}], Line[data_] :> data, All]~Flatten~1 produces the desired output, with all the branches as you said (and this would deserve a dedicated answer below). Maybe you made a typo in your comment? $\endgroup$
    – BowPark
    Commented Dec 10, 2019 at 12:13

1 Answer 1

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You might make a table as follows

lst1 = Table[{X, side1}, {X, 0.01, 10, 0.1}];

then transform the numbers into a format you need:

lst2 = lst1 // 
   NumberForm[#, NumberFormat -> (Row[{#, "e", #3}] &), 
     ExponentFunction -> (# &)] &;

and export it:

Export[NotebookDirectory[] <> "file.txt", lst2, "Table"] 

Do not forget to first save your notebook somewhere, to enable NotebookDirectory[] work.

Have fun!

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  • $\begingroup$ First of all, thank you. Apparently I have lst1 and lst2 equal in my code, so the output file has not the correct format. Maybe I'm doing something wrong? I also tried to put lst2 = lst1 // NumberForm ... all in the same line, but with no improvements. $\endgroup$
    – BowPark
    Commented Dec 9, 2019 at 12:09
  • $\begingroup$ Why do not you do exactly as I did. It worked for me, and should also work for you. $\endgroup$ Commented Dec 9, 2019 at 12:37
  • $\begingroup$ I did as you did: this is a screenshot and this is the output. Values in text file are not arranged as in the 3 sample line I posted in the question. $\endgroup$
    – BowPark
    Commented Dec 9, 2019 at 12:56

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