Hello everyone. I’m trying to use generated functions to write functions that would return the sum of the values of the nearest neighbors of given site in a multidimensional integer periodic lattice. For example: In a periodic 2D lattice, the sum of the values of the nearest neighbors of the site s would be lattice[mod1(s[1] - 1, size(lattice, 1)), s[2]] + lattice[mod1(s[1] + 1, size(lattice, 1)), s[2]] + lattice[s[1], mod1(s[2] - 1, size(lattice, 2))] + lattice[s[1], mod1(s[2] + 1, size(lattice, 2))] My attempt Reading through the examples provided in the Manual, I came up with the following: # Sum of nearest neighbors of site $s$ in a periodic integer lattice function square_lattice_nn_sum_impl(lattice::Type{Array{Int,dims}}, s::Type{NTuple{dims,Int}}) where dims # Accumulate final expression ex = :() # Loop on the dimensions for d in 1:dims # Indices for both nearest neighbors in the current dimension idx_prev_nn = :(mod1(s[$d] - 1, size(lattice, $d))) idx_next_nn = :(mod1(s[$d] + 1, size(lattice, $d))) # Fill indices before the current dimension idx_before = :() for k in d-1:-1:1 idx_before = :(s[$k], $idx_before) end # Fill indices after the current dimension idx_after = :() for k in d+1:dims idx_after = :($idx_after, s[$k]) end # Accumulate sum ex = :($ex + lattice[$idx_before $idx_prev_nn $idx_after] + lattice[$idx_before $idx_next_nn $idx_after]) end return :($ex) end # Extract generated function to the body of a regular function @generated function square_lattice_nn_sum(lattice::Array{Int,dims}, s::NTuple{dims,Int}) where dims square_lattice_nn_sum_impl(lattice, s) end For the 2D case, my program returns the following expression: julia> square_lattice_nn_sum_impl(Array{Int,2}, NTuple{2,Int}) :((() + lattice[() mod1(s[1] - 1, size(lattice, 1)) ((), s[2])] + lattice[() mod1(s[1] + 1, size(lattice, 1)) ((), s[2])]) + lattice[(s[1], ()) mod1(s[2] - 1, size(lattice, 2)) ()] + lattice[(s[1], ()) mod1(s[2] + 1, size(lattice, 2)) ()]) Which would be the desired result if it wasn’t for the several misplaced parentheses. My questions Is it possible to accumulate quoted expression without parentheses around them? Is there a better way of achieving this? Are generated functions even the right tool for this job? Thanks.

[image] evf: I’m trying to use generated functions to write functions that would return the sum of the values of the nearest neighbors of given site in a multidimensional integer periodic lattice. You don’t need a generated function for this. See: Seemingly unnecessary allocation within for loop - #8 by stevengj

There are other ways but I’d make arrays of expressions, and splat them. Rather than try to recursively build what aren’t really recursive expressions. julia> function new_short(lattice::Type{Array{Int,dims}}, s::Type{NTuple{dims,Int}}) where dims terms = map(1:dims) do d idx_prev_nn = :(mod1(s[$d] - 1, size(lattice, $d))) idx_next_nn = :(mod1(s[$d] + 1, size(lattice, $d))) idx_before = [:(s[$k]) for k in d-1:-1:1] term = :(lattice[$(idx_before...), $idx_prev_nn] + lattice[$(idx_before...), $idx_next_nn]) end return :(+($(terms...))) end; julia> new_short(Array{Int,2}, NTuple{2,Int}) :((lattice[mod1(s[1] - 1, size(lattice, 1))] + lattice[mod1(s[1] + 1, size(lattice, 1))]) + (lattice[s[1], mod1(s[2] - 1, size(lattice, 2))] + lattice[s[1], mod1(s[2] + 1, size(lattice, 2))])) julia> new_short(Array{Int,3}, NTuple{3,Int}) :((lattice[mod1(s[1] - 1, size(lattice, 1))] + lattice[mod1(s[1] + 1, size(lattice, 1))]) + (lattice[s[1], mod1(s[2] - 1, size(lattice, 2))] + lattice[s[1], mod1(s[2] + 1, size(lattice, 2))]) + (lattice[s[2], s[1], mod1(s[3] - 1, size(lattice, 3))] + lattice[s[2], s[1], mod1(s[3] + 1, size(lattice, 3))])) julia> function orig_short(lattice::Type{Array{Int,dims}}, s::Type{NTuple{dims,Int}}) where dims ex = :() # Trimming the original function to the same degree for d in 1:dims idx_prev_nn = :(mod1(s[$d] - 1, size(lattice, $d))) idx_next_nn = :(mod1(s[$d] + 1, size(lattice, $d))) idx_before = :() for k in d-1:-1:1 idx_before = :(s[$k], $idx_before) end ex = :($ex + lattice[$idx_before $idx_prev_nn] + lattice[$idx_before $idx_next_nn]) end return :($ex) end orig_short (generic function with 1 method) julia> orig_short(Array{Int,2}, NTuple{2,Int}) :((() + lattice[() mod1(s[1] - 1, size(lattice, 1))] + lattice[() mod1(s[1] + 1, size(lattice, 1))]) + lattice[(s[1], ()) mod1(s[2] - 1, size(lattice, 2))] + lattice[(s[1], ()) mod1(s[2] + 1, size(lattice, 2))])

Problem with parentheses around quoted expression in generated function

General Usage

stevengj December 19, 2021, 9:36pm 3

You don’t need a generated function for this. See: Seemingly unnecessary allocation within for loop - #8 by stevengj

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Problem with parentheses around quoted expression in generated function

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