[Beginner] Problem of :Vectors must be the same lengths

This is a Matlab beginner from Hong Kong.

I was trying to plot a graph with step function but it seems that there was something wrong with my code.

I have no idea of the error: vectors must be the same lengths plot.

The following is my code:

function practice2

to = -1:0.2:0;
t1 = 0:0.2:1;
t2 = 1:0.2:2;
t3 = 2:0.2:3;
t4 = 3:0.2:4;

yo = 0:NaN:0;
y1 =  2*t1;
y2 = -(2*t3) + 6;

t = [to t1 t2 t3 t4];
y = [yo y1 yo y2 yo];

plot (t,y)

[Jan]

Please post the complete error message in every case.

What is the purpose of 0:NaN:0?

Answer 1

[Cam Salzberger]

Hello Will,

If you take a look at the variables that are produced when you run the code, you might notice that yo is not a length-6 vector with all 0s, but instead a scalar NaN. What I think you meant to use instead was:

yo = zeros(size(to));

Also note that you are repeating the points at 0, 1, 2, and 3, since they are each contained in both the proceeding and subsequent "t" vectors.

I'd recommend just creating your "t" vector in one go, creating your "y" vector as all zeros, and then using logical indexing to modify the parts of the "y" vector that should be non-zero.

-Cam

[Will Hai]

I know the problem of repeating the points, however i don't get the idea of using logical indexing in my situation after i read through the hyperlink

it will be good if i can have more explanation from you

Thanks for your suggestion

[Cam Salzberger]

Well, you can make a single "t" and "y" vector with something like:

t = -1:0.2:4;
y = zeros(size(t));

Then you can only change the values of particular parts of the "y" vector, based on the values of "t":

y(t >= 0 & t < 1) = 2*t(t >= 0 & t < 1);
y(t >= 2 & t < 3) = 6-2*t(t >= 2 & t < 3);

This avoids the repeated points and cleans up the code a little, though it may be very slightly less time-efficient.

-Cam