splint.pas

来自「Delphi Pascal 数据挖掘领域算法包 数值算法大全」· PAS 代码 · 共 26 行

PROCEDURE splint(xa,ya,y2a: glnarray; n: integer;
       x: real; VAR y: real);
(* Programs using routine SPLINT must define the type
TYPE
   glnarray = ARRAY [1..n] OF real;
in the main routine. *)
VAR
   klo,khi,k: integer;
   h,b,a: real;
BEGIN
   klo := 1;
   khi := n;
   WHILE (khi-klo > 1) DO BEGIN
      k := (khi+klo) DIV 2;
      IF (xa[k] > x) THEN khi := k ELSE klo := k
   END;
   h := xa[khi]-xa[klo];
   IF (h = 0.0) THEN BEGIN
      writeln ('pause in routine SPLINT');
      writeln (' ... bad XA input'); readln END;
   a := (xa[khi]-x)/h;
   b := (x-xa[klo])/h;
   y := a*ya[klo]+b*ya[khi]+
      ((a*a*a-a)*y2a[klo]+(b*b*b-b)*y2a[khi])*(h*h)/6.0
END;