Hello, according to the plot(x,y) function syntax, the x and y vectors/arrays shoud have the same dimension. In Your case the 'time' has 89 elements and 'T' has maxiter=500. It will not work. Citing from help: "If x and y are vectors, plot(x,y) plots vector y versus vector x. x and y vectors should have the same number of entries."

You need to improe the algoritm binding the "T" and "time" togeather or just making the "time" the same length as "maxiter".

Best regards

Dariusz

It has nothing to do with the number of iterations. You are trying to plot temperature against time. And the dimensions of both are not same. Dariusz is right you have 89 elements in the time array. Whereas the temperature is calculated at 160 discrete steps. Just to check simply plot T(1,:) and other Ts without time.

Good luck

By the way, could you tell me how to define my time elements? In the other word, how do I know how many elements in my time array?

Hello again,

Just change a liitle bit the beginning of your code to that:

------------------------------------

clear;

dz =.001; //%each depth step is 0.001 meter

Nz = 5; //% Choose the number of depth steps (should go to at least 0.005 m)

Nt = 160; //% Choose the number of time steps

dt = (8*60*60)/Nt; //%Length of each time step in seconds (~ 6.3*10^3 seconds, or ~105 minutes)

K = 1.32*10^-7; //% "canonical" K is 10e-7 m^2/s

T = 20*ones(Nz+1,Nt+1); //%Create temperature matrix with Nz+1 rows, and Nt+1 columns

//% Initial guess is that T is 20 everywhere.

time_start=8; //Set start time

time_stop=18; //Set stop time

timestep=(time_stop-time_start)/(Nt); //Set time step

time = [time_start:timestep:time_stop]; //Define time matrix same dimension as temperature T

T(1,:) = 20; //%Set surface temperature

---------------------------------------

Remove the // comment if You need. In my case the plot shows however the temperature T is 20 everywhere.

Good luck

Hi, it seems like you don't know how to use the plot function. Check out help plot in matlab, you will get all details. Also, the multiple variables plotting is messed up, which should go as triplets, e.g. plot(x1,y1,c1,x2,y2,c2, ...).

The error says that the dimensions of your x and y vector in the plot are different, one is 89 other I suppose would be 161. Try out the following,

Try out plot(1:161,T(1,:),'r-.')

Also like to add one more comment that matlab coding is way easier if you just look at it as vector algebra. Also try out size(T) to know the variable size, when troubleshooting.

I think it says very clearly that the length of x and y variables are not the same so that the matlab doesn't know how to plot it. You should stick with this info and check them. Don't need to look up and down in your code to find the bug. Simply use "size" command to check every variables in your plot command. It should be every easy to locate the problem.

Matlab, or the Octave, is a good tool. But, just like every computer language, the users got to learn the "debug skill" to master the software.

I think it is independent of your software version. if the problem still exists, check your code. Maybe you define x or y twice (with different length) in your code.

For these sorts of problems the 'size' function is very useful in telling you how many elements are in your array. As soon as you see an error message with something like "vectors not the same length" or "index out of range" using the size function will instantly give you some clues as to what your code is actually doing.