in-place calculation

in-place calculation.ipynb

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      "source": "function update(u, h)\n    u + h*u\nend\n\nfunction iter_update(u, h, N)\n    for i in 1:N\n        u = update(u, h)\n    end\n    u\nend",
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      "source": "u = ones(1024^2)\nN = 1024\nh = 1/N\nu_new = iter_update(u, h, N)\nu_new[1:3]",
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            "text/plain": "3-element Array{Float64,1}:\n 2.7169557294664357\n 2.7169557294664357\n 2.7169557294664357"
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      "source": "@btime u_new = iter_update(u, h, N);",
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          "text": "  8.134 s (4096 allocations: 16.00 GiB)\n",
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      "source": "function update!(u, h)\n    @. u += h*u\nend\n\nfunction iter_update!(u, h, N)\n    for i in 1:N\n        update!(u, h)\n    end\nend",
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      "source": "u = ones(1024^2)\nN = 1024\nh = 1/N\niter_update!(u, h, N)\nu[1:3]",
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          "execution_count": 7,
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            "text/plain": "3-element Array{Float64,1}:\n 2.7169557294664357\n 2.7169557294664357\n 2.7169557294664357"
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      "source": "@btime iter_update!(u, h, N);",
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          "text": "  468.062 ms (0 allocations: 0 bytes)\n",
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