我是初学者小白，请给我解释这个知识点，---**Title:** The problem of distribution shift **Chart Description:** * **Type:** Line chart. * **Main Elements:** * **Coordinate Axes:** * Y-axis: Labeled "Estimated Advantage" and also has "ADVANTAGE" written along the axis. Arrows point upwards along the lower part of the axis. * X-axis: Labeled "(s,a)". * **Lines:** * A solid blue line, labeled "A^π" near the right end. It appears to represent a "True advantage of new policy". * A dashed blue line, labeled "Â^π" near the right end. * A solid red line, labeled "A^π'" near the right end. It also appears to represent a "True advantage of new policy". * A dashed red line, labeled "Â^π'" near the top left. * The blue lines are generally above the red lines for smaller values on the x-axis. The dashed lines ($ \hat{A} $) are estimations, while the solid lines ($ A $) represent the true advantage. There are two policies involved, π and π'. The labels suggest the red lines relate to π' and the blue lines relate to π. * **Points:** Several red crosses are marked along the X-axis. * **Labels and Annotations:** * "Estimated Advantage" is written near the top left, next to the Y-axis. * "True advantage of new policy" is written near the right side, next to the red and blue lines. * Labels for the lines: $ \hat{A}^{\pi'}, A^{\pi'}, \hat{A}^{\pi}, A^{\pi} $. * Axis labels: "ADVANTAGE", "(s,a)". **Other Relevant Text:** 我们的新策略希望一直向左移动 (Translation: Our new strategy hopes to keep moving to the left)