Write the output from ODE solve to a file

New to Julia
,
1

Hi All,

I’d like to know how to write the output from solve to a file. I’d prefer to write the solution sol to a
text or .mat file.

prob= ODEProblem(ODEFunction(fun, sparsity=sparsity,x0,(0.0,5.0))
@btime sol = solve($prob,QNDF())

Suggestions will be really appreciated.

1 Like
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Saving the solution as a BSON or CSV is probably the most convenient:
https://diffeq.sciml.ai/latest/features/io/#io
if you really want a plain txt file, you could do so with
I/O and Network · The Julia Language and a loop over sol.

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CSV is plain text. You can use dlmwrite from the DelimitedFiles standard library or, for greater performance, CSV.jl.

The MAT.jl package can write Matlab files, if you need that, but I wouldn’t recommend using that format except for interchange with Matlab. More generally, you can use HDF5.jl as a binary interchange format.

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@frankschae @stevengj

prob= ODEProblem(ODEFunction(fun, sparsity=sparsity,x0,(0.0,5.0))
@btime sol = solve($prob,QNDF())
df = DataFrame(sol)
println(df)
CSV.write("out.csv",df)

I tried the above. I’m not sure what’s the right way to access sol in the output @btime sol = solve($prob,QNDF()) .
I get the following error in the line df = DataFrame(sol) 

ERROR: LoadError: UndefVarError: sol not defined
Stacktrace:

Suggestions on the right way to access the data present in the variable sol will be really helpful.

5

I think your code would work by putting the @btime macro to the rhs

sol = @btime solve($prob,QNDF())

However, if you have benchmarked the solvers already and if you only want to store the solution of the ODE solve and output a rough timing at the same time, then you could also use @time :

sol = @time solve(prob,QNDF())

which won’t run the solve call several times.