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I started working on Mathematica today. I'm trying to save the result of a loop in a file as a column, very simple to do, but hard for someone who doesn't know Mathematica syntax. Here is my code:

For[i = 1/10, i <= 4, i += (1/1000), 
    l = NIntegrate[(-1 + 0.707106781186547`/(-x^2 E^-x^2 + 0.5`)^0.5`)/x, {x, ∞, i}];
    Save["data.dat",l]
]

but obviously, this code is not working, it seems Save only works with strings. I have tried data streams, but I'm getting aborted each time I try.

How can I save the output from NIntegrate into a data file, in a loop?

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  • $\begingroup$ Changed the data.dat for a string with the same name and It's working, but the file has in each row a l=value. Is there a way to just save the value? $\endgroup$
    – nosumable
    Jul 22, 2022 at 2:49

1 Answer 1

Reset to default
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It is better to avoid For loops. And why not just use Export? And try to not use l for variable. Not a good choice as it looks like 1.

SetDirectory[NotebookDirectory[]]
ClearAll[x];
range = Range[1/10,4,1/10];
data  = NIntegrate[(-1+0.707106781186547`/(-x^2 E^-x^2+0.5`)^0.5`)/x,{x,Infinity,#}]&/@range;
Export["data.txt",data]

This is how the file looks like

enter image description here

Update

For Fortran format use

SetDirectory[NotebookDirectory[]]
ClearAll[x];
range = Range[1/10,4,1/10];
data  = NIntegrate[(-1+0.707106781186547`/(-x^2 E^-x^2+0.5`)^0.5`)/x,{x,Infinity,#}]&/@range;
data  = FortranForm[#]&/@data ;

Export["data.txt",data]

The file looks like

enter image description here

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  • $\begingroup$ Hi, u are totally right, those mistakes are from a noob like me! By the way, I need the last values without that format because they are not readable in other languages like python, for example. Is there an easy way to change that? $\endgroup$
    – nosumable
    Jul 22, 2022 at 3:02
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    $\begingroup$ I do not understand what you mean by I need the last values without that format ? Can you give an example of what you mean? Do you mean Python does not understand -5.626766190483531*^-8 ? $\endgroup$
    – Nasser
    Jul 22, 2022 at 3:03
  • $\begingroup$ Sure, those values are not readable in other languages like python (number*^ exponent) Python functions struggle with that syntax. Is there a way to write those values for example like 1.0232e-4, which is readable in python? $\endgroup$
    – nosumable
    Jul 22, 2022 at 3:09
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    $\begingroup$ @nosumable update for Fortran format. Hopefully Python can read it now. $\endgroup$
    – Nasser
    Jul 22, 2022 at 3:19
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    $\begingroup$ Thanks! U are awesome, that is what I was searching too! Have a good day. $\endgroup$
    – nosumable
    Jul 22, 2022 at 3:21

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