2楼: Originally posted by dingd at 2016-10-08 19:50:27
可以试试用1stOpt计算。假如k范围=【1,4】，变幅0.1

LoopConstant k=;
Variable x=,y=0,y'=;
Plot x,y,y';
ODEFunction y''=-k*cos(y);


c261.jpg

c262.jpg
...

LoopConstant k=[1:0.1:4];
Variable x=[0,1],y=0,y'=[,0];
Plot x[x],y,y';
ODEFunction y''=-k*cos(y);

function dy = magFun(x,y)
  global k;
  dy = zeros(2,1);
  dy(1) = y(2);
  dy(2) = -k*cos(y(1));
end
  

function res = magBC( ya,yb )
  res = [ ya(1); yb(2) ];
end
  
  function magSol
  clear,clc
  global k; %全局变量k
  yt=[];    %存储要绘图的y数据
  x = linspace(0,1,10);
  for k=1:5
  solinit = bvpinit(x,[1 0]);
  sol = bvp4c(@magFun,@magBC,solinit);
  
  y = deval(sol,x);
  yt=[yt;y(1,:)];
  end
  plot(x,yt)
  legend('1','2','3','4','5')