Построение графиков методами Эйлера и Рунге-Кутта уравнение второго порядка - Pascal ABC

uses graphABC;
var i,j,b:integer; x0,y0,y2,x,y,F,p,h,y1:real;
begin
 setpencolor(clblue);
 SetpenWidth(3);
 Line(40,200,600,200);
 Line(300,10,300,400);
 
 p:=0.04;
 h:=0.01;
 y1 := 0;
 y2 := 0.45;
 b := 3;
 
 x :=0;
 y := 0;
 while (x < b) do begin
 setpencolor(clred);
 SetpenWidth(1);
  F := -p*x*y2-y1*y1; 
  
  y1 := y1 + F*h;
  y2 :=y2 + y1*h;
  x := x + h;
  i := 300 + round (100*x);
  j := 200 - round (y1*350);
  circle (i,j,1);
  i := 300 + round (100*x);
  j := 200 - round (y2*350);
  circle (i,j,1);
 end;
end.

uses graphABC;
var i,j,b:integer; x0,y0,y01,h2,y1,x1,y2,k1,k2,k3,k4,k11,k21,k31,k41,x,y,F,p,h:real;
begin
 setpencolor(clblue);
 SetpenWidth(3);
 Line(40,200,600,200);
 Line(300,10,300,400);
 
 p := 0.04;
 h := 0.01;
 y1 := 2;
 y2 := 0;
 b := 5;
 x := 0;
 y := 0;
 x0 := 0;
 y0 := 2;
 y01 := 0;
 h2 := h / 2;
 //y1 := y0;
 x1 := x0;
 //y2 := y01;
 
while (x1 < b) do begin
 setpencolor(clred);
 SetpenWidth(1);
 
 k1 := -p*x1*y2-y1*y1;
 k2 := -p*(x1+h2)*(y2+h2*k1)-(y1+h2*k1)*(y1+h2*k1);
 k3 := -p*(x1+h2)*(y2+h2*k2)-(y1+h2*k2)*(y1+h2*k2);
 k4 := -p*(x1+h)*(y2+h*k3)-(y1+h2*k3)*(y1+h2*k3);
 y1 := y1 + (k1 + 2 * (k2 + k3) + k4) * h / 6;
 k11 := y1 ; //y2 + y1*h;
 k21 := {-p*(x1 + h2) *y2-(}y1+h2*k11{)*(y1+h2*k11); //y2 + (y1+h2*k11)*h};
 k31 := {-p*(x1 + h2)*y2-(}y1+h2*k21{)*(y1+h2*k21); //y2 + (y1+h2*k21)*h};
 k41 := {-p*(x1+h)*y2-(}y1+h*k31{)*(y1+h*k31); //y2 + (y1+h2*k31)*h};
 y2 := y2 + (k11 + 2 *(k21 + k31) + k41) * h / 6;
 x1 := x1 + h;
 
  //F := -p*x*y2-y1*y1; 
  //y2 :=y2 + y1*h;
  //y1 := y1 + F*h;
  //x := x1 + h;
    
  i := 300 + round (50*x1);
  j := 200 - round (y1*50);
  circle (i,j,1);
  i := 300 + round (50*x1);
  j := 200 - round (y2*50);
  circle (i,j,1);
 end;
end.