mirror of
https://github.com/L-yang-yang/cugenopt.git
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72 lines
2.3 KiB
Python
72 lines
2.3 KiB
Python
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"""
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Knapsack-specific custom operators.
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These operators exploit knapsack structure (value/weight ratio awareness)
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to make more informed bit-flip decisions.
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"""
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from cugenopt.operators import CustomOperator
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_KNAPSACK_GREEDY_FLIP = CustomOperator(
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name="knapsack_greedy_flip",
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code=r"""
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int row = 0;
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int sz = sol.dim2_sizes[row];
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if (sz < 2) return false;
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const float* weights = prob->d_weights;
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const float* values = prob->d_values;
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int pos = rand_int(rng, sz);
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if (sol.data[row][pos] == 0) {
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float ratio = (weights[pos] > 0.001f)
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? values[pos] / weights[pos] : 0.0f;
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if (ratio > 0.5f || curand_uniform(rng) < 0.3f) {
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sol.data[row][pos] = 1;
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return true;
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}
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} else {
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float ratio = (weights[pos] > 0.001f)
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? values[pos] / weights[pos] : 1e6f;
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if (ratio < 0.5f || curand_uniform(rng) < 0.3f) {
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sol.data[row][pos] = 0;
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return true;
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}
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}
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return false;
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""",
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encoding="binary",
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initial_weight=0.8,
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)
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_KNAPSACK_SWAP_RATIO = CustomOperator(
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name="knapsack_swap_ratio",
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code=r"""
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int row = 0;
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int sz = sol.dim2_sizes[row];
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if (sz < 2) return false;
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const float* weights = prob->d_weights;
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const float* values = prob->d_values;
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int in_item = -1, out_item = -1;
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for (int t = 0; t < 8; t++) {
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int p = rand_int(rng, sz);
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if (sol.data[row][p] == 1 && in_item < 0) in_item = p;
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if (sol.data[row][p] == 0 && out_item < 0) out_item = p;
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if (in_item >= 0 && out_item >= 0) break;
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}
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if (in_item < 0 || out_item < 0) return false;
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float in_ratio = (weights[in_item] > 0.001f)
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? values[in_item] / weights[in_item] : 1e6f;
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float out_ratio = (weights[out_item] > 0.001f)
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? values[out_item] / weights[out_item] : 0.0f;
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if (out_ratio > in_ratio || curand_uniform(rng) < 0.2f) {
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sol.data[row][in_item] = 0;
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sol.data[row][out_item] = 1;
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return true;
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}
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return false;
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""",
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encoding="binary",
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initial_weight=0.8,
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)
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knapsack_ops = [_KNAPSACK_GREEDY_FLIP, _KNAPSACK_SWAP_RATIO]
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