How to plot multiple curves on the same screen for different values of "b" with bvp4c solver?

Question

Ke Le 2022-9-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1803320-how-to-plot-multiple-curves-on-the-same-screen-for-different-values-of-b-with-bvp4c-solver

评论： Star Strider 2022-9-13

I am trying to draw multiple plots for multiple "b" values on a the same screen. The code is here. Any kind of help would be great.

function solution

b=1;

R=2;

pp=[1; 2; 3];

for i=1:numel(pp)

b=pp(i);

end

dYdX = @(X,Y) [Y(2); Y(3); (R/3*Y(2)).*(-2*Y(1).*Y(3)+Y(2)^.2)];

res = @(ya,yb) [ya(1)-b; ya(2); yb(2)];

SolYinit = bvpinit(linspace(0,100,1000),[0; 0; 0;]);

Fsol = bvp4c(dYdX, res, SolYinit);

X1 = Fsol.x;

Y1 = Fsol.y;

figure (1)

plot(X1, Y1(2,:), 'LineWidth', 2);

hold on

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Answer 1

Star Strider 2022-9-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1803320-how-to-plot-multiple-curves-on-the-same-screen-for-different-values-of-b-with-bvp4c-solver#answer_1051685

在 MATLAB Online 中打开

The problem is that the initial conditions are uniformly zero, so any change in ‘b’ will not be evident since the entire result will be zero otherwise. Also, the entire code needs to be inside the loop.

The ‘res’ function will inherit the value of ‘b’ from the workspace, so it does not have to be passed as an extra parameter, however it could be. It would then be:

res = @(ya,yb,b) [ya(1)-b; ya(2); yb(2)];

and the call too it in the bvp4c call would then be:

Fsol = bvp4c(dYdX, @(ya,yb)res(ya,yb,b), SolYinit);

That also works.

Try this —

b=1;

R=2;

pp=[1; 2; 3];

for i=1:numel(pp)

b=pp(i);

dYdX = @(X,Y) [Y(2); Y(3); (R/3*Y(2)).*(-2*Y(1).*Y(3)+Y(2)^.2)];

res = @(ya,yb) [ya(1)-b; ya(2); yb(2)];

SolYinit = bvpinit(linspace(0,100,1000),[0; 0; 0]+eps);

Fsol = bvp4c(dYdX, res, SolYinit);

X1{i} = Fsol.x;

Y1{i} = Fsol.y;

end

figure (1)

hold on

for k = 1:numel(pp)

plot(X1{k}, Y1{k}(2,:), 'LineWidth', 2, 'DisplayName',sprintf('p = %d',pp(k)))

end

hold off

legend('Location','best')

The initial conditions need to be something other than zero in order that the output not be uniformly zero, so I added eps to nudge them away from zero.

.