"Error using plot, A numeric or double convertible argument is expected" Having vector issues with my symbols and I don't know why!

Nlayers=20;                     %number of layers in the lung
syms z;
subs(z, input('Enter layer number'));  % specific layer

TLC=7;                          %total lung capacity
Htot=0.16;                      %total lung height, metres
plung=300;                      %lung density kg/m3
Vad=0.15;                       %Volume of the anatomical dead space
g=9.81;                         %Gravitational acceleration
Hz=(Htot/Nlayers)*(z);          %height of each layer
Nalvtot=300;                    %total number of alveoli
Nalvz=Nalvtot/Nlayers;          %Number of alveoli in a layer

Valvmax=(TLC-Vad)/Nalvtot;        %maximum volume
syms r;
Valvz=(4/3)*pi*r^3;             %volume of the alveolus in layer z
Pe=(0.42-log(1/((0.98*Valvz/Valvmax)+0.015)-1)*0.22);    %Elastic pressure
y=15*10^-3;                      %surface tension

Vtotal=Vad+symsum(Nalvz*Valvz, z, 0, 20);

Py=(2*y)/r;                    %Pressure due to surface tension

Ventilator_pressure;
Phydroz=plung*g*Hz;             %Hydrostatic gradient at a given lung height
Pcw=0.71-log((0.95*TLC)/((Vtotal/TLC)-(0.22*TLC))-1)*0.58;   %Pressure component of the chest wall

[r, z] = solve(Py+Pe == Pvent-Phydroz-Pcw);

figure;
ezplot(r);

This is my code, but when i run it, it says there's an error, i think its because its making hte symbols into vectors which aren't equal in size, but im not sure why its doing that! Help!

[David Young]

I wonder why you are using the symbolic toolbox. Is there a reason for z and r to be syms? Could you try doing it as an ordinary numerical computation (i.e. no syms)?

[sophie webster]

not particularly, it was suggested that i do so, I just want to be able to construct a number of graphs using all of the variables above. How would i need edit it to removes the syms other than those statements?

Answer 1

[Star Strider]

If you want to keep your code symbolic, see if the ezplot function will work.

[sophie webster]

Hi, I've tried this - ive edited my code on the question to show what ive inputted but its coming up blank, any ideas? I dont mind not making the code symbolic, i just dont know how to change it

[Stephane Magnam]

I also have the same issue with this following code:

v1=11*t^2-5*t;
dv1=diff(v1);
t1=[0:0.5:10];
plot(t1,dv1);

Any help?

[CS Researcher]

What is t?

[Walter Roberson]

You have no made any connection between the t of the equation and the t1 of the locations to plot at

plot(t1, subs(dv1, t, t1))

[Stephane Magnam]

So I have a set of 3 equations for velocity in function of time. Each of them is associated with a range of time 't'. I am trying to plot on separate graphs the acceleration and the second derivative of the velocity. That's why I have this confusion about t and t1, t2, and t3. Here are the info:

dt=0.5;
t=[0:dt:50];  
v1=11*t^2-5*t;
v2=1100-5*t;
v3=50*t-2*((t-20)^2);
dv1=diff(v1);
t1=[0:0.5:10];
figure(1);
plot(t1,subs(dv1, t, t1));
hold on;
dv2=diff(v2);
t2=[20:0.5:35];
plot(t2,subs(dv2, t, t2));
hold on;
dv3=diff(v3);
t3=[35:0.5:50];
plot(t3,subs(dv3, t, t3));

I realize that my code does not necessarily have a lot of sense, but it is just an intuitive way to approach the problem. t1, t2, t3, in the code are the ranges of t for equations v1, v2, and v3 respectively. Any easier way to approach this is appreciated? PS: Using subs made it work but it appears that the graph I obtain does not make a lot of sense since I'm getting 3 separate lines.