MATLAB plot not showing.

Question

N/A 2019-4-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/455559-matlab-plot-not-showing

回答： Pallavi Bharati 2020-3-10

I tried plotting two graphs with the following:

with the following output:

The second one (plot(x,1./(4*x-8'))) is showing just fine, but not the first one (plot x,y1). Y1 is a 1x1001 double array. Why is that, and how can i fix the problem?

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madhan ravi 2019-4-11

在 MATLAB Online 中打开

Since the OP removed the orginal content according to the other question the content seems to be:

clear all ;
 
close all;
 
f=@(x,y1,y2) y2;
 
g=@(x,y1,y2) 1/4*y1-8;
 
%shooting method inntialization
 
initialize=[-5:.05:0];
 
for kk=1:length(initialize)
 
%delta x=1
 
x(1)=1;
 
y1(1)=10;
 
y2(1)=initialize(kk);
 
h=0.001;
 
x_initial=x(1);
 
xmaxvalue=2;
 
n=(xmaxvalue-x_initial)/h;
 
%runge kutta iterations using shooting method
 
    for i=1:n
 
        k0 = h*f(x(i),y1(i),y2(i));
 
        l0 = h*g(x(i),y1(i),y2(i));
 
        k1 = h*f(x(i)+(1/2)*h,y1(i)+(1/2)*k0,y2(i)+(1/2)*l0);
 
        l1 = h*g(x(i)+(1/2)*h,y1(i)+(1/2)*k0,y2(i)+(1/2)*l0);
 
        k2 = h*f(x(i)+(1/2)*h,y1(i)+(1/2)*k1,y2(i)+(1/2)*l1);
 
        l2 = h*g(x(i)+(1/2)*h,y1(i)+(1/2)*k1,y2(i)+(1/2)*l1);
 
        k3 = h*f(x(i)+h,y1(i)+k2,y2(i)+l2);
 
        l3 = h*g(x(i)+h,y1(i)+k2,y2(i)+l2);
 
        x(i+1) = x_initial+i*h;
 
        y1(i+1) = double(y1(i)+(1/6)*(k0+2*k1+2*k2+k3));
 
        y2(i+1) = double(y2(i)+(1/6)*(l0+2*l1+2*l2+l3));
 
    end
 
yy1(kk)=y1(end);
 
end
 
p=interp1(yy1',initialize',1/4);
 
x(1)=1;
 
y1(1)=1/4
 
y2(1)=p;
 
h=0.001;
 
x_initial = x(1);
 
xmaxvalue=2;
 
n=(xmaxvalue-x_initial)/h;
 
for i=1:n
 
k0=h*f(x(i),y1(i),y2(i));
 
l0=h*g(x(i),y1(i),y2(i));
 
k1=h*f(x(i)+(1/2)*h,y1(i)+(1/2)*k0,y2(i)+(1/2)*l0);
 
l1=h*g(x(i)+(1/2)*h,y1(i)+(1/2)*k0,y2(i)+(1/2)*l0);
 
k2=h*f(x(i)+(1/2)*h,y1(i)+(1/2)*k1,y2(i)+(1/2)*l1);
 
l2=h*g(x(i)+(1/2)*h,y1(i)+(1/2)*k1,y2(i)+(1/2)*l1);
 
k3=h*f(x(i)+h,y1(i)+k2,y2(i)+l2);
 
k3=h*g(x(i)+h,y1(i)+k2,y2(i)+l2);
 
x(i+1)=x_initial+i*h;
 
y1(i+1)=double(y1(i)+(1/6)*(k0+2*k1+2*k2+k3));
 
y2(i+1)=double(y2(i)+(1/6)*(l0+2*l1+2*l2+l3));
 
end
 
%plot the solution
figure
title('shooting method')
xlabel('t')
ylabel('y(t)')
plot(x,y1)
hold on 
 
% make your second plot
figure
(plot(x,1./(4*x-8)'))
 
legend('numerical solution','exact solution')

Rena Berman 2019-5-13

(Answers Dev) Restored edit

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Answer 1

Jon 2019-4-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/455559-matlab-plot-not-showing#answer_370038

在 MATLAB Online 中打开

The problem is that the second plot is replacing (overwriting) the first one in the figure window. If you open up a new figure, before making the second plot you will avoid this problem. Even better, create a new figure for each plot in case you already had another one there you didn't want to overwrite, So for example:

% make new figure
figure
% make the first plot
(plot x,y1)
% make another figure
figure
% make your second plot
(plot(x,1./(4*x-8')))

Also a couple of other side comments. I agree with Stephen's comment, it is better to use the code button to insert code. Also in your specific plot command, I'm not sure what you are intending with 4*x - 8'. In this case the transpose operator (') will only be applied to the scalar value of 8, which will not have any effect.