Matlab Plot can't work.
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Hi Guys,
Below is my code, and I have a quesion, when I modify the plot function from plot(x,z,'-*r') to plot(x,z), the figure can't show, Does anyone know why?
clc
clear
clc
f = @(x,y,z) 1/y*(y+z); %where k = 1 for y''
g = @(x,y,z) z ; %for y'
h = 0.1;
x= 0;
z= 1;
y= 1;
%value of y at x = %0.2f and z = 0.2%f is %f\n
for i = 1:25
k1 = h.*f(x,y,z);
j1 = h.*g(x,y,z);
k2 = h.*f(x+h/2,y+k1/2,z+j1/2);
j2 = h.*g(x+h/2,y+k1/2,z+j1/2);
k3 = h.*f(x+h/2,y+k2/2,z+j2/2);
j3 = h.*g(x+h/2,y+k2/2,z+j2/2);
k4 = h.*f(x+h,y+k3,z+j3);
j4 = h.*g(x+h,y+k3,z+j3);
k = (k1+2*k2+2*k3+k4)./6;
j = (j1+2*j2+2*j3+j4)./6;
x = x + h;
z = z + j;
y = y + k;
fprintf('i = %8.0f, y = %8.6f, x = %8.2f, z = %8.6f\n',i,y,x,z);
plot(x,z,'-*r')
hold on
plot(x,y,'-ob')
end
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采纳的回答
KSSV
2022-7-13
编辑:KSSV
2022-7-13
clc
clear
clc
f = @(x,y,z) 1/y*(y+z); %where k = 1 for y''
g = @(x,y,z) z ; %for y'
h = 0.1;
x= 0;
z= 1;
y= 1;
%value of y at x = %0.2f and z = 0.2%f is %f\n
figure
hold on
for i = 1:25
k1 = h.*f(x,y,z);
j1 = h.*g(x,y,z);
k2 = h.*f(x+h/2,y+k1/2,z+j1/2);
j2 = h.*g(x+h/2,y+k1/2,z+j1/2);
k3 = h.*f(x+h/2,y+k2/2,z+j2/2);
j3 = h.*g(x+h/2,y+k2/2,z+j2/2);
k4 = h.*f(x+h,y+k3,z+j3);
j4 = h.*g(x+h,y+k3,z+j3);
k = (k1+2*k2+2*k3+k4)./6;
j = (j1+2*j2+2*j3+j4)./6;
x = x + h;
z = z + j;
y = y + k;
fprintf('i = %8.0f, y = %8.6f, x = %8.2f, z = %8.6f\n',i,y,x,z);
plot(x,z,'-*r')
plot(x,y,'-ob')
end
The suggested way is this:
clc
clear
clc
f = @(x,y,z) 1/y*(y+z); %where k = 1 for y''
g = @(x,y,z) z ; %for y'
h = 0.1;
N = 25 ;
x = zeros(N,1) ;
y = zeros(N,1) ;
z = zeros(N,1) ;
x(1)= 0;
z(1)= 1;
y(1)= 1;
%value of y at x = %0.2f and z = 0.2%f is %f\n
for i = 2:25
k1 = h*f(x(i-1),y(i-1),z(i-1));
j1 = h*g(x(i-1),y(i-1),z(i-1));
k2 = h*f(x(i-1)+h/2,y(i-1)+k1/2,z(i-1)+j1/2);
j2 = h*g(x(i-1)+h/2,y(i-1)+k1/2,z(i-1)+j1/2);
k3 = h*f(x(i-1)+h/2,y(i-1)+k2/2,z(i-1)+j2/2);
j3 = h*g(x(i-1)+h/2,y(i-1)+k2/2,z(i-1)+j2/2);
k4 = h*f(x(i-1)+h,y(i-1)+k3,z(i-1)+j3);
j4 = h.*g(x(i-1)+h,y(i-1)+k3,z(i-1)+j3);
k = (k1+2*k2+2*k3+k4)./6;
j = (j1+2*j2+2*j3+j4)./6;
x(i) = x(i-1) + h;
z(i) = z(i-1) + j;
y(i) = y(i-1) + k;
fprintf('i = %8.0f, y = %8.6f, x = %8.2f, z = %8.6f\n',i,y(i),x(i),z(i));
end
plot(x,z,'-*r')
hold on
plot(x,y,'-ob')
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