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2547Numeric Weakest-Link Alpha 16A node has leaf error 18 if pruned into a single leaf. Its current subtree has training error 10 and 3 leaves. What is the weakest-link alpha for pruning this subtree?机器学习简单数值题未尝试免费2549Penalized Split Decision on a Regression Node 18A regression leaf has SSE 260. Splitting it would reduce child SSE to 230. If the complexity penalty is 12 per extra leaf, should you keep the split?机器学习中等数值题未尝试免费2550Optimal Leaf Label Under Asymmetric Trading CostsA classification leaf contains 6 positive cases and 14 negative cases. Predicting positive costs 1 per false positive, while predicting negative costs 4 per false negative. Which class should the leaf predict to minimize expected leaf loss?机器学习困难derivation未尝试面试订阅2551Why Pre-Pruning Can Miss a Good Two-Step Split 9Why can an aggressive pre-pruning rule reject a first split that looks weak locally even though it would unlock a much better second-level structure?机器学习简单essay未尝试免费2552Which Split Becomes Best After a Perturbation 19Split A originally has gain 1.20 and split B has gain 1.05. After one row is corrected, A loses 0.10 gain while B gains 0.08. Which split is now best?机器学习中等数值题未尝试免费2553Maximum Balanced Depth Numerically 20A tree starts with 96 observations at the root and every split is perfectly balanced. If each leaf must contain at least 12 observations, what is the maximum possible depth?机器学习中等数值题未尝试面试订阅2554Cost-Sensitive Leaf Label 21A leaf contains 7 positives and 13 negatives. Predicting negative incurs false-negative cost 4 on each hidden positive, while predicting positive incurs false-positive cost 1 on each hidden negative. Which class should the leaf predict?机器学习中等数值题未尝试面试订阅2555Best Valid Split Under a Minimum-Leaf ConstraintThree candidate splits on the same node have Gini gains 0.18, 0.16, and 0.11, with smaller-child sizes 3, 4, and 7 respectively. If the minimum allowed leaf size is 4, which split is actually chosen?机器学习困难derivation未尝试面试订阅2556Grouped Values and Feasible Thresholds 22A sorted feature has five distinct-value blocks of sizes [3, 5, 2, 4, 6], and splits are allowed only between distinct-value blocks. If each child leaf must contain at least 6 observations, how many legal thresholds exist?机器学习简单数值题未尝试免费2557Why Small Data Perturbations Can Rewrite the Whole Tree 10Why are deep decision trees often called unstable learners?机器学习简单essay未尝试免费2559Expected Misroutes From a Surrogate SplitA surrogate split agrees with the primary split on 34 of 40 training cases where both features are present. If 12 production cases are missing the primary split feature and are routed by the surrogate, what is the expected number of misroutes?机器学习困难derivation未尝试面试订阅2560Global Weight Rescaling Leaves Split Ranking Unchanged 5If every sample weight in a node is multiplied by the same constant c>0, how does each candidate split's weighted impurity decrease change?机器学习困难derivation未尝试面试订阅2566Choose the Weakest-Link Node to Prune 24Node A would have leaf error 12 if pruned, while its current subtree has error 7 and 3 leaves. Node B would have leaf error 9 if pruned, while its current subtree has error 6 and 2 leaves. Which node is the weaker link and should be pruned first under cost-complexity pruning?机器学习简单数值题未尝试免费2568Compare Penalized Tree Options 25A parent node left uncut has SSE 70. A 2-leaf split gives total SSE 44. A 3-leaf subtree gives total SSE 36. If the complexity penalty is 10 per extra leaf relative to the uncut node, which option has the lowest penalized objective?机器学习中等数值题未尝试免费2570Surrogate Split Agreement Rate 8A primary split is missing for some rows, so a surrogate split is trained on the M rows where the primary feature is observed. If it sends A of those rows to the same side as the primary split, what is its agreement rate?机器学习困难derivation未尝试面试订阅2572Numeric Ensemble Variance 22Each tree has variance 9, pairwise correlation 0.2, and the forest has 25 trees. What is the variance of the forest average?机器学习简单数值题未尝试免费2577Why OOB Is Unsafe for Grouped or Temporal Data 13Why can out-of-bag error be misleading when rows are linked by entity or time rather than being exchangeable?机器学习中等essay未尝试面试订阅2581Why Random-Forest Regression Extrapolates Poorly 16Why does random-forest regression usually fail to extrapolate a trend far beyond the training range?机器学习简单essay未尝试免费2589Bagged MSE When Bias Stays Fixed 7Assume each tree has the same squared bias b 2 and prediction noise floor nu, while bagging only changes the variance term according to the equicorrelated-tree formula. Derive the bagged test MSE with B trees.机器学习困难derivation未尝试面试订阅2592Effective Independent Tree Count 8Define B eff by matching the correlated-forest variance sigma 2 [rho + (1-rho)/B] to the variance sigma 2 / B eff of averaging independent trees. Derive B eff.机器学习简单derivation未尝试免费