修改Mathematica代码实现指定区间的函数曲线分段绘制

修改后的Mathematica代码 #

eqn[d_Integer?NonNegative, r_, B_, A_, nmax_Integer?Positive] := 
  Sum[Exp[-n*\[Lambda]]*(1 - r)^n Exp[n*k^2 - k^2*A (HarmonicNumber[n + d] - HarmonicNumber[d]) + B*k*HarmonicNumber[n]], {n, 1, nmax}] == -1 + Exp[\[Lambda]]/r;
AValues = {2};
BValues = {1};

Show[
  Block[{$MaxExtraPrecision = 500},
    ContourPlot[
      Evaluate@Table[eqn[0, 0.25, B, A, 100], {A, AValues}, {B, BValues}],
      {k, -2, 2}, {\[Lambda], -0.5, 3.5},
      FrameLabel -> (Style[#, 14] & /@ {k, "\!\(\*SubscriptBox[\(\[Lambda]\), \(r\)]\)(k)"}),
      RotateLabel -> False,
      PlotPoints -> 100,
      MaxRecursion -> 4,
      AspectRatio -> 1/GoldenRatio,
      PlotLegends -> Automatic,
      GridLines -> {{-0.5, 1.0}, {0}},
      GridLinesStyle -> Directive[Gray, AbsoluteThickness[1], Dashed],
      (* 限制蓝色曲线仅在k=-0.5到1.0之间显示 *)
      RegionFunction -> Function[{k, λ}, -0.5 <= k <= 1.0]
    ]
  ],
  (* 黑色曲线拆分为两段，仅显示虚线外区域 *)
  Plot[k^2 + Log[0.75], {k, -2, -0.5}, PlotStyle -> {Black}],
  Plot[k^2 + Log[0.75], {k, 1.0, 2}, PlotStyle -> {Black}],
  PlotLegends -> Placed[
    {"\!\(\*SubscriptBox[\(\[Lambda]\), \(0\)]\)(k)+ln(1-r)"},
    {.5, .7}
  ]
]

修改说明 #

• 给ContourPlot添加RegionFunction参数，明确指定仅在-0.5 <= k <= 1.0范围内绘制蓝色曲线；
• 将原本单段的黑色曲线Plot拆分为两个区间：k∈[-2,-0.5]和k∈[1.0,2]，确保只在两条虚线外侧显示；
• 保留原代码的图例、网格线、格式等其他设置，保证整体视觉风格一致。

内容的提问来源于stack exchange，提问作者caren