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I often do long calculations in Mathematica. If I’ve got the time, I’ll keep the kernel active and do all the fun plotting, animating, basic playing-around with the results right when I’m thinking about it. However, often I need to quit and move on to other things on my todo list. That’s what this post is all about.

## .m files

Any result in Mathematica can be saved to a .m file. The syntax is pretty basic:

sol=First[NDSolve[{y''[t]==-y[t]-beta y'[t], y[0]==1, y'[0]==0}, y, {t,0,10}]];

Export["filepath . . ./cool.m", sol]

Then later you can import the file like so:

solnew=Import["same m file location"];

Plot[y[t]/.solnew, {t,0,10}]

Note how I saved the result of an NDSolve command and later was able to use it to make a plot.

## web storage

What's extra cool is that you can save your .m files to a web server because you can do things like this:

coolthing=Import["http://euclid.hamline.edu/~arundquist/research/hartree/listofsolsHLi.m"]

and be able to use results of calculations anywhere. I especially like this when I'm going to work on a project both at home and at work as the import command syntax doesn't need to change. I used to do this with Dropbox where both my machines would have an up-to-date copy of the .m files but I still had to change the syntax because my dropbox folder tends to be in different locations on different machines.

Thanks a lot for this information. I have been simulating a robotic manipulator. and NDSOLVE can take a while. Glad to know i can save the results

Glad I could help, Fabian. I recently ran into an interesting problem, though. The NDSolve took a long time and I had to go, so I did the .m file trick. However, it took a long time because it was taking incredibly small steps. The range was something like {t,0,5} modeling 20 charged particles interacting in a box. However, the .m file was over 200 MB! That’s just to save all the interpolate data. That was a little bigger than I had bargained for.