it does not plot V1,V2 untill I put * in plot order. why?
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Hi guys, I want to plot s/th in matlab. But my matlab does not give me the right answer until I put * in plot in V1,V2,x1 plot. why?
My code is:
clc;
clear all;
% syms x1(t)
% syms x2(t)
% syms x3(t)
% syms x4(t)
x1(1)=57.5;
x2(1)=8.5;
x3(1)=0.051;
x4(1)=4.8;
deltat=10^-3;
B=[0.0015 -0.0015 -6.9*10^-12;-5.9*10^-5 -9*10^2 5.9*10^-11;3.46*10^-5 5.2*10^-5 3.24*10^-11;-0.0167 0.0239 -1.0733*10^-9];
u=[32;32;80];
for i=1:100
% (x1(i+1)-x1(i))/deltat=-1.5*x1(i)+x2(i);
% (x2(i+1)-x2(i))/deltat=(x1(i)+x2(i))*sin(x1(i))-3*x2(i);
x1(i+1)=(3.7*10^-15*x1(i)+7.6*10^-6*x2(i))*deltat+x1(i);
x2(i+1)=(-4*10^-16*x1(i)-6.5*10^-5*x2(i)-2.8)*deltat+x2(i);
x3(i+1)=(2.37*10^-16*x1(i)-0.142*x3(i))*deltat+x3(i);
x4(i+1)=(-8.15*10^-14*x1(i)-0.5535*x2(i)+18.21*x3(i)+0.0833*x4(i))*deltat+x4(i);
V1(i)=0.5*(x1(i).^2+x2(i).^2+x3(i).^2+x4(i).^2);
V2(i)=0.5*x1(i).^2+x2(i).^2+x3(i).^2+x4(i).^2;
end
for i=1:100
figure(1)
plot(x1(1,:),x2(1,:))
hold on;
plot(x1(1,1),x2(1,1),'bo') % starting point
hold on;
plot(x1(1,end),x2(1,end),'ks') % ending point
hold on;
figure(2);
plot(i,x1(1,i),'*-')
hold on;
figure(3)
plot(i,V1(1,i),'*-')
hold on
figure(4)
plot(i,V2(1,i),'*-')
hold on;
end
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채택된 답변
azam ghamari
2019년 4월 14일
댓글 수: 1
Walter Roberson
2019년 4월 14일
The default is not to use any marker. When you use '*-' you tell it to use * as a Marker. plot will plot markers when you tell it to plot individual points. plot() needs at least two adjacent finite points in order to plot a line, but it only needs isolated finite points in order to plot markers.
추가 답변 (2개)
Image Analyst
2019년 4월 12일
In MATLAB, type this control-a (to select all), control-i (to fix indenting), control-c (to copy). Then paste back here, highlight and click the code icon.
You say "I want to plot s/th". What are s and th? I don't see them in the code. The rest of the code runs, but it's a bit unnecessary to have it plot every single point one at a time unless you were going to put a break point in the code to watch it slowly.
When you plot a single element of V1 or V2, at a particular i value.....
If you don't use * to place a marker, and only use - (which connects two data points with a line), then you will see nothing because you're plotting only a single point, not two points that can be connected by a line.
댓글 수: 3
Walter Roberson
2019년 4월 14일
Please read https://www.mathworks.com/matlabcentral/answers/455433-plot-not-appearing-in-the-axes#comment_692085 which explains why you do not see anything.
Image Analyst
2019년 4월 14일
Yes, using '-' will connect the points, but you're not plotting multiple points in any of your calls to plot V1 or V2. Like I said, you're plotting only ONE point, NOT two or more:
plot(i,V1(1,i),'*-') % Plot one single value, V1(1,i)
The above will plot a marker * but no line since only one point is being plotted, not two or more.
azam ghamari
2019년 4월 14일
댓글 수: 1
Walter Roberson
2019년 4월 14일
Your i is a scalar because you are in a for i loop. plot(i,V2(1,i),'*-') is plot() of a scalar i value and a scalar value extracted from V2. This is a request to plot() only one point in that one call. plot() never creates a line unless you plot() at least two adjacent finite values in the same call . For example, plot(i:i+1, V2(1,i:i+1), '*-') would be a request to plot two adjacent points and it would be willing to create a line between the two.
You should remove the
figure(4)
plot(i,V2(1,i),'*-');
hold on
from the loop, and then after the loop you should put in
figure(4)
plot(1:100, V2(1,1:100), '*-')
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