Problem in plotting the nonlinear differential equation using bvp4c

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Muhammad Fahad 2016-4-7

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https://ww2.mathworks.cn/matlabcentral/answers/277708-problem-in-plotting-the-nonlinear-differential-equation-using-bvp4c

评论： Walter Roberson 2016-4-7

I selected three different nonlinear ordinary differential equations and solve then by using builtin command bvp4c;but all times MATLAB gives me the plot similar to "upward parabola".I want to ask why this happend?why the behavior of graph is almost same for three totally different problems? thank you

Problem 1:

function yp=myodefun(t,y)
yp=zeros(2,1);
yp(1)=y(2);
yp(2)=(1/8)*(32+2*t^3-y(1)*y(2));
function res=mybcfun(ya,yb)
res=zeros(2,1);
res(1)=ya(1);
res(2)=yb(1);
clear all
clc
solinit = bvpinit([1  3],[17 43/3]);
sol = bvp4c(@myodefun,@mybcfun,solinit);
xint = linspace(1,3);
yint = deval(sol,xint);
plot(xint,yint(1,:))

Problem 2:

function yp=odefun(t,y)
yp=zeros(2,1);
yp(1)=y(2);
yp(2)=2*(y(1))^3;
function res=bcfun(ya,yb)
res=zeros(2,1);
res(1)=ya(1);
res(2)=yb(1);
clear all
clc
solinit = bvpinit([-1  0],[0.5 1/3]);
sol = bvp4c(@odefun,@bcfun,solinit);
xint = linspace(-1,0);
yint = deval(sol,xint);
plot(xint,yint(1,:))

Problem 3:

function yp=odefun(t,y)
yp=zeros(2,1);
yp(1)=y(2);
yp(2)=-(y(2))^2-y(1)+log(t);
function res=bcfun(ya,yb)
res=zeros(2,1);
res(1)=ya(1);
res(2)=yb(1);
clear all
clc
solinit = bvpinit([1  2],[0 log(2)]);
sol = bvp4c(@odefun,@bcfun,solinit);
xint = linspace(1,2);
yint = deval(sol,xint);
plot(xint,yint(1,:))