plot graph for multiple values for one of the variables on the same axis (and in different colours)

I want to plot multiple lines for different values of r2 % outer radius of sphere, m

Please can someone help me?

r1=18e-2; % inner radius of sphere, m

>> r2=24e-2; % outer radius of sphere, m

>> k=0.034; % thermal conductivity of sphere wall, W /(m C)

>> bc1=40; % temperature at inner sphere wall, deg C

>> bc2=-81; % temperature at outer sphere wall, deg C

>> n=100*2*2*2*2; % number of unknown temperatures between the two radii

>> m=(r2-r1)/(n+1); % step size: difference between two consecutive difference pointa, m

>>

>> %%%%%%%%%% GENERATION OF MATRIX A5

>> for i=1:n

r(i)=r1+i*m;

a(i,i)=-2*r(i)^2/m^2;

if(i==1)

a(i,i+1)=(r(i)^2/m^2 +r(i)/(m));

end

if((i>1)&&(i<n))

a(i,i-1)=(r(i)^2/m^2 -r(i)/(m));

a(i,i+1)=(r(i)^2/m^2 +r(i)/(m));

end

if(i==n)

a(i,i-1)=(r(i)^2/m^2 -r(i)/(m));

end

end

>> %%%% BOUNDARY CONDITION MATRIX GENERATION OF MATRIX B5

>> b(1,1)=-(r(1)^2/m^2 -r(i)/(m))*bc1;

>> b(n,1)=-(r(n)^2/m^2 +r(i)/(m))*bc2;

>>

>> t=inv(a)*b;

>>

>> temp(1,1)=bc1;

>> temp(2:n+1,1)=t(1:n);

>> temp(n+2,1)=bc2;

>>

>> radius(1,1)=r1;

>> radius(2:n+1,1)=r(1:n);

>> radius(n+2,1)=r2;

>>

>> figure(1)

>> plot(radius,temp)

>> xlabel('Radius, m','fontsize',20,'fontweight','b')

>> ylabel('Temperature, (^{o}C)','fontsize',20,'fontweight','b')

r2 values:[24e-2,30e-2,36e-2]

thank you for your time.

Answer 1

[KSSV]

You have to initilaize the variables inside the loop. Read about initliaing an array in aloop.

r1=18e-2;   % inner radius of sphere, m
r2=24e-2;   % outer radius of sphere, m
k=0.034;   % thermal conductivity of sphere wall, W /(m C)
bc1=40;   % temperature at inner sphere wall, deg C
bc2=-81;   % temperature at outer sphere wall, deg C
n=100*2*2*2*2;   % number of unknown temperatures between the two radii
R2 = [24e-2,30e-2,36e-2] ;
for j = 1:length(R2)
    r2 = R2(j) ;
    m=(r2-r1)/(n+1);   % step size: difference between two consecutive difference pointa, m
    %%%%%%%%%% GENERATION OF MATRIX A5
    for i=1:n
        r(i)=r1+i*m;
        a(i,i)=-2*r(i)^2/m^2;
        if(i==1)
            a(i,i+1)=(r(i)^2/m^2 +r(i)/(m));
        end
        if((i>1)&&(i<n))
            a(i,i-1)=(r(i)^2/m^2 -r(i)/(m));
            a(i,i+1)=(r(i)^2/m^2 +r(i)/(m));
        end
        if(i==n)
            a(i,i-1)=(r(i)^2/m^2 -r(i)/(m));
        end
    end
    %%%% BOUNDARY CONDITION MATRIX GENERATION OF MATRIX B5
    b(1,1)=-(r(1)^2/m^2 -r(i)/(m))*bc1;
    b(n,1)=-(r(n)^2/m^2 +r(i)/(m))*bc2;
    
    t=inv(a)*b;
    
    temp(1,1)=bc1;
    temp(2:n+1,1)=t(1:n);
    temp(n+2,1)=bc2;
    
    radius(1,1)=r1;
    radius(2:n+1,1)=r(1:n);
    radius(n+2,1)=r2;
    R(:,j) = radius' ;
    T(:,j) = temp' ;
end
figure(1)
plot(R,T)
xlabel('Radius, m','fontsize',20,'fontweight','b')
ylabel('Temperature, (^{o}C)','fontsize',20,'fontweight','b')