I am trying to plot a function with iteration of a variable

%%

a = .0022; %m

d = .05*a; %m

viscosity_p = 1.2; %cP

viscosity_c = 3.5; %cP

dpdz1 = -10; %mmHg

dpdz2 = -1.3; %kPa

t = 0;

for r =0:.01:a

Vc(r) = ((r.^2 - (a-d)^2)/(4*viscosity_c))*dpdz1;

Vp(r) = ((r.^3 - ((a-d)^2)*r)/(4*viscosity_p*d))*dpdz1;

t = t+1;

end

plot(Vc,r)

Answer 1

[Star Strider]

Try this:

a = .0022; %m
d = .05*a; %m
viscosity_p = 1.2; %cP
viscosity_c = 3.5; %cP
dpdz1 = -10; %mmHg
dpdz2 = -1.3; %kPa
t = 0;
rv = linspace(0,a);
for k = 1:numel(rv)
    r = rv(k);
    Vc(k) = ((r.^2 - (a-d)^2)/(4*viscosity_c))*dpdz1;
    Vp(k) = ((r.^3 - ((a-d)^2)*r)/(4*viscosity_p*d))*dpdz1;
    t = t+1;
end
plot(Vc,rv)

In MATLAB, indices must be integers greater than 0, so using ‘r’ as an index will not work Also, since ‘a’ is only slightly greater than the 0.01 increment, the colon-described ‘r’ vector contains only one value. The linspace call creates 100 elements in ‘rv’ by default, and as many as you want if you supply a third argument to it.

Answer 2

[David Hill]

Not sure what t is, but you do not need a for-loop.

r = 0:.01:a;
Vc = ((r.^2 - (a-d)^2)/(4*viscosity_c))*dpdz1;
plot(Vc,r);