20250610

279-3.py

@@ -0,0 +1,25 @@
+def ClassicRK(x0,y0,h,xk,fxy):
+    k1=k2=k3=k4=0
+    result = [(x0,y0)]
+    while x0<=xk:
+        k1 = fxy(x0,y0)
+        k2 = fxy(x0+h/2,y0+h*k1/2)
+        k3 = fxy(x0+h/2,y0+h*k2/2)
+        k4 = fxy(x0+h,y0+h*k3)
+        y0 += h*(k1+4*k2+k3)/6
+        x0 += h
+        result.append((x0,y0))
+    return result
+
+
+if __name__=="__main__":
+    x0 = 0
+    y0 = -1
+    fxy = lambda x,y: x + y
+    real_fx = lambda x: -x-1
+    h = 0.1
+    xk = 2
+    result = ClassicRK(x0, y0, h, xk, fxy)
+    print("x\ty\t\treal_y")
+    for x, y in result:
+        print(f"{x:.2f}\t{y}\t{real_fx(x)}")