matplotlib · Genlovy-Hoo · Jun 11, 2023 · Jun 11, 2023 · Jun 12, 2023 · Jun 12, 2023
diff --git a/galleries/examples/subplots_axes_and_figures/twinx_align.py b/galleries/examples/subplots_axes_and_figures/twinx_align.py
@@ -0,0 +1,73 @@
+"""
+===============================================
+Let twin-axis aligned at the specified position
+===============================================
+
+Let the left-axis and right-axis aligned at the specified position.
+
+In some data that need twin-axis plot, a point at left-axis and
+another point at right-axis have same meaning, they should be aligned.
+For example, we plot netvalue curve of a portfolio at twin-left-axis
+and profit raito curve at twin-right-axis, the point 1.0 at the
+left-axis and the point 0.0 at the right-axis both mean the begin
+state of the portifolio, so they should be aligned.
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+# Sim data
+net_value = np.array([1.0, 0.98, 0.95, 1.0, 1.22, 1.25, 1.29, 1.34,
+                      1.39, 1.18, 1.14, 1.04, 1.36, 1.41, 1.5, 1.56,
+                      1.56, 1.57, 1.26, 1.35])
+gain_pct = np.array([0.0, -0.02, -0.05, 0.0, 0.02, 0.04, 0.07,
+                     0.12, 0.16, 0.18, 0.14, 0.04, 0.05, 0.08,
+                     0.15, 0.2, 0.2, 0.21, 0.26, 0.35])
+
+
+def twinxalign(ax_left, ax_right, v_left, v_right):
+    """
+    Let the position `v_left` on `ax_left`
+    and the position `v_right` on `ax_right` be aligned
+    """
+    left_min, left_max = ax_left.get_ybound()
+    right_min, right_max = ax_right.get_ybound()
+    k = (left_max-left_min) / (right_max-right_min)
+    b = left_min - k * right_min
+    x_right_new = k * v_right + b
+    dif = x_right_new - v_left
+    if dif >= 0:
+        right_min_new = ((left_min-dif) - b) / k
+        k_new = (left_min-v_left) / (right_min_new-v_right)
+        b_new = v_left - k_new * v_right
+        right_max_new = (left_max - b_new) / k_new
+    else:
+        right_max_new = ((left_max-dif) - b) / k
+        k_new = (left_max-v_left) / (right_max_new-v_right)
+        b_new = v_left - k_new * v_right
+        right_min_new = (left_min - b_new) / k_new
+    ax_right.set_ylim([right_min_new, right_max_new])
+    return ax_left, ax_right
+
+
+def plot_example(align=False):
+    """Plot sim data"""
+    plt.figure(figsize=(10, 7))
+    ax1 = plt.subplot(111)
+    ax1.plot(net_value, "-k")
+    ax1.axhline(1, c="k", lw=1, ls="--")
+    ax1.set_ylabel("NetValue(black)", fontsize=16)
+    ax2 = ax1.twinx()
+    ax2.plot(gain_pct, "-b")
+    ax2.axhline(0, c="r", lw=1, ls="--")
+    ax2.set_ylabel("GainPct(blue)", fontsize=16)
+    if align:
+        twinxalign(ax1, ax2, 1, 0)
+        plt.title("aligned", fontsize=16)
+    else:
+        plt.title("not align", fontsize=16)
+    plt.show()
+
+
+plot_example()
+plot_example(align=True)