How do I plot my differential equation on Matlab?

Here is my MATLAB code.

syms v(t) t C1
inflow = 3
peri = .4
Vin = 40
outflow = 4
p = .3
qip = p*inflow
p2 = (v)/(Vin+(inflow-outflow)*(t))
qop = p2*outflow
eqn = diff(v) == qip-qop
S = dsolve(eqn);
pretty(S)

Vp = Vin*peri;
    tval = 0;

    D = Vp-S
    Value = subs(D,tval)
    C1 = solve(Value)
    
    tval2 = 7;
    Value2 = subs(D,tval2)
    C2 = solve(Value2)

    V = p*(Vin-tval2)+C1*(Vin-tval2)^(4)

I'm trying to plot Vp and V, but whenever I do, the figure just shows a straight line. It should be something like (tval,Vp) and (tval2,V). Please help, thank you!

Answer 1

[Star Strider]

Of copurse it’s going to be a straight line!

After evaluating the functions, look at ‘(tval,Vp)’ and ‘(tval2,V)’. They are all constants!

syms v(t) t C1
inflow = 3

inflow = 3

peri = .4

peri = 0.4000

Vin = 40

Vin = 40

outflow = 4

outflow = 4

p = .3

p = 0.3000

qip = p*inflow

qip = 0.9000

p2 = (v)/(Vin+(inflow-outflow)*(t))

p2(t) = 

qop = p2*outflow

qop(t) = 

eqn = diff(v) == qip-qop

eqn(t) = 

S = dsolve(eqn);

pretty(S)

           4   3 t
C1 (t - 40)  - --- + 12
                10

figure
fsurf(S, [-5 5  0 75])
xlabel('Initial Condition')
ylabel('t')

Vp = Vin*peri

Vp = 16

    tval = 0;

    D = Vp-S

D = 

    Value = subs(D,tval)

Value = 

    C1 = solve(Value)

C1 = 

    
    tval2 = 7;
    Value2 = subs(D,tval2)

Value2 = 

    C2 = solve(Value2)

C2 = 

    V = p*(Vin-tval2)+C1*(Vin-tval2)^(4)

V = 

.