rk4.txt

《Delphi常用数值算法集》的配书源码

procedure RK4(Y,DYDX:array of real;N:integer;X,H:real;var YOUT:array of real);
var
    YT, DYT, DYM:array[0..10] of real; HH,H6,XH:real;
    I:integer;
begin
    HH:=H * 0.5;
    H6:=H / 6;
    XH:=X + HH;
    For I:=1 To N do
        YT[I]:=Y[I] + HH * DYDX[I];
    DERIVS(XH, YT, DYT);
    For I:=1 To N do
        YT[I]:=Y[I] + HH * DYT[I];
    DERIVS(XH, YT, DYM);
    For I:=1 To N do
    begin
        YT[I]:=Y[I] + H * DYM[I];
        DYM[I]:=DYT[I] + DYM[I];
    end; 
    DERIVS(X + H, YT, DYT);
    For I:=1 To N do
        YOUT[I]:=Y[I] + H6 * (DYDX[I] + DYT[I] + 2 * DYM[I]);
end;