Differential equation not working

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Reji G 2022-10-17

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https://ww2.mathworks.cn/matlabcentral/answers/1829283-differential-equation-not-working

评论： Walter Roberson 2022-10-21

在 MATLAB Online 中打开

I wanted to implement the equation below:

I wrote the program as follows. But nothing showing up in the plot.

clc; close all; clear all;
t=0.01:0.001:10;
V=575*sin(2*pi*t);
I=100*sin(2*pi*t);
P0=250;
syms V(t)
syms I(t)
ode = diff(V) == (V*I)*diff(I)-((V/0.01)*(((V*I)/P0)-1));
VSol(t) = dsolve(ode);
fplot(VSol(t),[0 10]);

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Torsten 2022-10-17

编辑：Torsten 2022-10-17

Why do you specify I and V and then try to solve a differential equation for V ? If you know that V =575*sin(2*pi*t), you don't need to solve a differential equation.

Further, in order to plot a possible solution for V, you will have to specify an initial condition, e.g. V at t=0.

Reji G 2022-10-18

What should I modify in the code ?

If V(0)=0.1, then ?

I'm not knowing much of these. That's why came to help center

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回答（1 个）

Torsten 2022-10-18

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I = @(t)100*sin(2*pi*t);;

dIdt = @(t) 2*pi*100*cos(2*pi*t);

V0 = 0.1;

fun = @(t,V,I,dIdt) V/I(t)*dIdt(t)-V/0.01*(V*I(t)/250-1.0);

[T,V] = ode45(@(t,V) fun(t,V,I,dIdt),0.01:0.001:10,V0);

plot(T,V)

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Reji G 2022-10-21

Thank you Torsten.

For I = @(t)100*sin(2*pi*t); your first code itself is working fine.

My concern is I = @(t)100*sin(100*pi*t); (in place of 1Hz if I give 50 HZ(2->100)), the program is showing 5 errors. I want a plot for I = @(t)100*sin(100*pi*t).