This is a question regarding the use of “=” signs in Julia. I can do the following for-loop in MATLAB for ii = 1 : dt ηp1 = shallowwave1D(ηn,ηm1,r); ηm1 = ηn; ηn = ηp1; end Can the same be done in Julia? Or will there be some issues with copies where whatever I do to ηn changes ηm1 (see…

for ii = 1 : dt ηp1 = shallowwave1D(ηn,ηm1,r); ηm1 = ηn; ηn = ηp1; end I am really confused about this loop. Why is the looping variable ii not used inside the loop itself?

for ii = 1 : dt ηp1 = shallowwave1D(ηn,ηm1,r); ηm1 = deepcopy(ηn); ηn = deepcopy(ηp1); end It would really help if you can tell us what is ηp1 ηn Is it a scalar (ie Float64), a struct , an array , a Dict or a set?

They are all supposed to be numeric arrays (i.e. something like [1,2,3,4]).

If they are arrays of arrays then use deepcopy to be really safe if they are just arrays of scalars (ie array of Float64), you can use copy

Noted! Thanks! If I didn’t use copy or deepcopy, what would happen?

Noted! Thanks! If I didn’t use copy or deepcopy, what would happen? Then you get aliasing julia> a = [1 2 3] 1×3 Array{Int64,2}: 1 2 3 julia> b = a 1×3 Array{Int64,2}: 1 2 3 julia> b[2]=666 666 julia> b 1×3 Array{Int64,2}: 1 666 3 julia> a 1×3 Array{Int64,2}: 1 666 3

May also be helpful to see this behavior julia> a = [1, 2, 3] 3-element Array{Int64,1}: 1 2 3 julia> b = a[:] 3-element Array{Int64,1}: 1 2 3 julia> b[1] 1 julia> b[1] = 4 4 julia> b 3-element Array{Int64,1}: 4 2 3 julia> a 3-element Array{Int64,1}: 1 2 3 In the above example, a d…

Thank you so much for the help!

In this specific case, you don’t need to copy. ηn = ηp1 does not mutate ηn, but re-binds it to another array. So, ηm1 is not affected. It would only be affected if you modified ηn in-place, e.g. with copyto!(ηn, ηp1).

In addition to @Vasily_Pisarev ’s answer (with which I fully agree), I would like to add that I think a common idiom to perform what (I think) you want to do would be something like: # Initialize input arrays ηm1 = something ηn = something # Preallocate an array for the result ηp1 = similar(ηn) # …

Assignments, Copies and Deepcop

General Usage Performance

rdeits November 5, 2019, 4:55pm 14

For example, in this post we were able to make the original user’s code over 3000 times faster by avoiding accidental copies and memory allocation.

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Assignments, Copies and Deepcop

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