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Answers for “为什么当函数平坦时牛顿法会失败?”

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Understand why

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Newton's method fails when the function is flat because the local slope (derivative) is zero or near-zero. Since the method relies on drawing a tangent line and finding its x-intercept, a horizontal tangent does not intersect the x-axis at a useful new point, preventing progress toward the root.

Conditions: The function is locally flat at the current point.; The slope is too small or zero to provide a useful Newton step.

Find a method

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Newton's method uses an iterative geometric procedure. Starting from an initial guess, it moves vertically to the function graph, computes the local slope, draws a tangent line, and takes that tangent's x-intercept as the next guess.

Conditions: An initial guess x must be chosen.; The function has a usable slope at the current point.; The tangent line must intersect the horizontal zero line to produce the next guess.