I am sort of getting fuzzy on how to apply syntactic loop fusion from https://www.juliabloggers.com/more-dots-syntactic-loop-fusion-in-julia/

Is this:

`nnp.theta[hl] .= nnp.theta[hl] .+ (hp.alphaovermb .* (hp.lambda .* nnp.theta[hl]))`

the same as this:

`nnp.theta[hl][:] = nnp.theta[hl] .+ (hp.alphaovermb .* (hp.lambda .* nnp.theta[hl]))`

theta[hl] is the weight matrix for one hidden layer in a neural net. Note that nnp.theta is an array containing the weight matrices for each layer. Indexing on [hl] gets the matrix for one layer, in this case 128 x 256. I pre-allocate all of the weight matrices and want to update in place. When I first did this way back with Julia 0.6, I used the second form. Then, I switched to the first form. What I forget is whether, in addition to fusing the loop for the right-hand-side, this also assigns in place to the left-hand-side.

I tested each way and got same results and timing essentially the same so the answer must be yes, these do the same thing. I use this all over the place to update weights, biases, and training data. Just trying to make sure I’ve done reasonable optimization. I also tried a manual loop but must have done something wrong as the results were different and it was much slower.

For minibatch training, I replaced a sliced based approach (each minibatch updating a pre-allocated “slice” holder) with a view based approach. I seem to think this made things slower. It’s a fair bit of work to go back, but I put back some of the slice-based plumbing to do that comparison. It seemed much slower.

I save timings of all runs, so I can go back and see if my memory is right…