Plotting with a for loop

I have a for loop and need to plot my final results. I have the hold on command in my code, but I still get only one point on my plot. What am I doing wrong?

Answer 1

[Star Strider]

You probably have the plot command inside your loop.

Guessing as to your code, but it is best to do something like this instead :

for k = 1:n
    x(k) = k;
    y(k) = sin(x(k));
end

figure(1)
plot(x, y)

[Jayme]

My plot is outside the the for loop.

for x=0:.001:.1

     T=(((erfc(w)-exp(v+u^2)*erfc(w+u))*(T_infinity-T_i))+T_i)
end

plot(x,T);shg

[Star Strider]

It seems ‘T’ is not a function of ‘x’, and ‘T’ is not being saved as a vector in the loop. Are ‘w’, ‘v’, or ‘u’ related to ‘x’ in any way?

Try this (or something like it with the appropriate value for ‘w’):

x=0:.001:.1;
for k = 1:length(x)
    w = x(k);
    T(k)=(((erfc(w)-exp(v+u^2)*erfc(w+u))*(T_infinity-T_i))+T_i);
end
plot(x,T);shg

[Jayme]

There are a few lines where I set up the dummy variables u and w, which are functions of x. They are located in the for loop, but I had deleted them accidently with my comments from my code when I pasted it into my previous comment.

for x=0:.001:.1

   u=((h*sqrt(alpha*t))/k)

   v=((h*x)/k)

   w=(x/(2*sqrt(alpha*t)))

   T=(((erfc(w)-exp(v+u^2)*erfc(w+u))*(T_infinity-T_i))+T_i)
end

plot(x,T);shg

[Star Strider]

I’m lost. Are ‘h’, ‘u’, ‘v’, ‘t’ and ‘w’ vectors the same length as ‘x’? (BTW, where did my ‘k’ loop disappear to? In your loop here, ‘x’ isn’t doing anything except iterating through the same calculations 100 times without changing them.) You have to subscript ‘T’ as well in the loop in order to have it the same length as ‘x’.

[Jayme]

The variables h, k, alpha, and t are all constant. Thus u is constant. The variables v and w are just dummy variables that are defendant on x.

I am trying to solve a heat transfer problem. I have a given set of temperatures (T_i and T_infinity), a convection rate (h), and a material (which dictates k and alpha). I know the amount of time the heat is exchanged (t) and I need to plot the temperature (T) across the material--at different distances (x).

Here is my entire code:

% Given

 T_i=25;

 T_infinity=800;

 h=20;

 t=325;

%Find T

%Table A.3 for Oak Wood

 rho=720;

 k=.16;

 c=1255;

%calculations

 alpha=k/(rho*c);

hold on;

for x=0:.001:.1

   %dummy varriables

   u=((h*sqrt(alpha*t))/k)

   v=((h*x)/k)

   w=(x/(2*sqrt(alpha*t)))

   %Solve for T

   T=(((erfc(w)-exp(v+u^2)*erfc(w+u))*(T_infinity-T_i))+T_i)

end

plot(x,T);shg

[Image Analyst]

Have an index counter instead of x like you have.

x = 0 : 0.001 : 1
for k = 1 : length(x)
   u=((h*sqrt(alpha*t))/k);
   v=((h*x(k))/k);
   w=(x/(2*sqrt(alpha*t)));
   T(k)=(((erfc(w)-exp(v+u^2)*erfc(w+u))*(T_infinity-T_i))+T_i);
end
plot(x, T, 'b-', 'LineWidth', 3);
grid on;

By the way, check to see if the k in the denominator inside the loop is supposed to be the loop index. I don't know where that k came from.

[Jayme]

When I use this method, I have a completely blank graph. Where as before, I could get a point.

[Star Strider]

SUCCESS!

You don’t need the loop:

T_i=25;
T_infinity=800;
h=20;
t=325;
rho=720;
k=.16;
c=1255;
alpha=k/(rho*c);
u=((h*sqrt(alpha*t))/k);

x=0:.001:.1;
v=((h*x)/k);
w=(x/(2*sqrt(alpha*t)));
v=((h*x)/k);
w=(x/(2*sqrt(alpha*t)));
T=(((erfc(w)-exp(v+u^2).*erfc(w+u))*(T_infinity-T_i))+T_i);

plot(x,T);shg

produces:

Answer 2

[Esther Maria Ribezzo]

I have the same problem!!

for i=1:length(asse_x);

MLSE=(norm(AI_concatenated-(S*(A_TOT(:,i))))).^2;

plot(asse_x(i),MLSE, '*')

hold on

end

Answer 3

[Moh'd Allouzi]

for k = 1:n

x(k) = k;

y(k) = sin(x(k));

end

figure(1)

plot(x, y)

Answer 4

[alaa sleem]

cp=1.2

ta=30

hhv=50000

tex=130

k=1

for lamda =(.8,.1,1.5)

A_F(k)=lamda*x*(32+3.76*28)/(n*12+m*1)

if lamda < 1

N_CO2= x*((2*lamda)-1)-(m/4);

n_CO= x*((2*lamda)-1)-(m/4);

n_h2o=m/2;

n_n2=(lamda*x*3.76);

Total=N_CO2+n_CO+n_n2+n_h2o;

Xi_co2(k)=N_CO2/Total;

Xi__CO(k)=n_CO/Total;

Xi_h2o(k)=n_h2o/Total;

Xi_N2(k)=n_n2/Total;

#______________________________________________lean_____________________________________________

else lamda >= 1

N_CO2= n;

n_O2= x*(lamda-1);

n_h2o=m/2;

n_n2=(lamda*x*3.76);

Total=N_CO2+n_O2+n_n2+n_h2o;

Xi_co2(k)=N_CO2/Total;

Xi_o2(k)=n_O2/Total;

Xi_h2o(k)=n_h2o/Total;

Xi_N2(k)=n_n2/Total;

end

t_f(k) = ta+(hhv/((1+lamda)*cp))

eta(k)= ((1+lamda)*cp*(t_f-tex))/hhv

lamd_list(k)=lamda

k=k+1

end

fig1 = figure(1);

ax1 = axes('Parent', fig1);

A_F_plot = plot(lamd_list, total_util);

%concentration

plot(lamd_list,Xi_co2)

hold.on

plot(lamd_list(:lenght(Xi_o2)),Xi_o2)

hold.on

plot(lamd_list(:lenght(Xi__CO)),Xi__CO)

hold.on

plot(lamd_list,Xi_h2o)

hold.on

plot(lamd_list,Xi_N2)

hold.off

%air fuel

plot(lamd_list,A_F)

%temp

plot(lamd_list,A_F)