plot doesn`t work (probably unrelated to the code )

2018 8 16
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更新时间：2018 8 20
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%start
clear all
syms y(t) a Vp
Vp = 1;
Dy=diff(y(t));
Dt=diff(t);
t=0:0.0001:0.4999;
pulseRC1=dsolve(a*(Dy/Dt)+y==Vp,y(0)==0);
pulseRC1=eval(pulseRC1);
plot(t,pulseRC1);
hold on
t= 0.5000:0.0001:1;
pulseRC2=dsolve((Dy/Dt)*0.1+y==0,y(0.5)==Vp);
pulseRC2=eval(pulseRC2);
plot(t,pulseRC2);
hold off
pulseRc=[pulseRC1,pulseRC2];
xlabel('t')
ylabel('pulseRC')
}
%end
These are the matlab codes I have been working on.
I typed this set of codes by hand and when I run it, matlab only returns a matrix of numeric values in command window. On the other hand, the other set of code which is exactly the same but typed on a different computer runs perfectly well on my computer.//
So far I have tried to reinstall the matlab and updated to the latest version. The problem stay the same.//
What is strange to me is that the fact if I copy the working code to the current script, instead of returning a plot graph, it only return a set of numeric answers.

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Rik
Rik 2018-8-16
What does the following line of code return as output?
which plot -all
Ziming Huang
Ziming Huang 2018-8-20
>> which plot -all
built-in (C:\Matlab\toolbox\matlab\graph2d\plot)
C:\Matlab\toolbox\matlab\polyfun\@alphaShape\plot.m % alphaShape method
C:\Matlab\toolbox\matlab\polyfun\@polyshape\plot.m % polyshape method
C:\Matlab\toolbox\matlab\bigdata\@tall\plot.m % tall method
C:\Matlab\toolbox\matlab\graphfun\@digraph\plot.m % digraph method
C:\Matlab\toolbox\matlab\graphfun\@graph\plot.m % graph method
C:\Matlab\toolbox\signal\signal\@dspdata\plot.m % dspdata method
C:\Matlab\toolbox\stats\classreg\@LinearModel\plot.m % LinearModel method
C:\Matlab\toolbox\matlab\timeseries\@timeseries\plot.m % timeseries method
returned those

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 采纳的回答

Star Strider
Star Strider 2018-8-16

0 个投票

For ‘pulseRC1’, you either need to define ‘a’, or give it a range and use the fsurf (link) function. For ‘pulseRC2’, you need to use fplot (link). I used fplot for both plots here. You also do not need eval. The Toolbox does all this for you.
Try this:
syms y(t) a Vp
Vp = sym(1);
Dy=diff(y(t));
Dt=diff(t);
% t=0:0.0001:0.4999;
a = sym(42); % Supply Correct Value
pulseRC1=dsolve(a*(Dy/Dt)+y==Vp,y(0)==0)
fplot(pulseRC1, [0 0.5]);
hold on
% t= 0.5000:0.0001:1;
pulseRC2=dsolve((Dy/Dt)*0.1+y==0,y(0.5)==Vp);
fplot(t,pulseRC2, [0.5 1]);
hold off
pulseRc=[pulseRC1,pulseRC2];
xlabel('t')
ylabel('pulseRC')

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Haritha
Haritha 2018-8-16
编辑：Haritha 2018-8-16

1 个投票

your t value is in double format and pulseRC1 is in sym format. keep both the formats as same. Then plot the values. In your file pulseRC1 is showing empty matrix.

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Ziming Huang
Ziming Huang 2018-8-20
Thank you Haritha! actually the pulseRC1 is returning matrix with values instead of empty matrix.

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