Beginner Matlab function only plotting zero

Question

I have been thrown in the deep end in one of my Signals classes. I am trying to learn Octave so that I can do the Matlab assignments required by the professor at home (I have not had any education in Matlab yet).

I have been reading as much as I can but I cannot seem to figure out why this function only seems to return 0. I think I am missing something fundamental but I don't know what.

t = [-1:0.1:5];

% (a): The Unit-step Function u(t)
function u = u (t)
    if(t >= 0)
        u = 1;
    else
        u = 0;
    end
end

plot(t, u(t));

Because u in your function is a scalar not a vector. Try initializing u = zeros(size(t)), and u(t>=0) = 1. That should do it. — kedarps
– kedarps, Commented Jun 7, 2017 at 1:44

eyllanesc · Accepted Answer · 2017-06-07 01:45:53Z

1

The problem arises because the function enters a vector and returns a scalar, so plot draws erroneously.

One solution:

A possible solution is to create the new vector with zeros (), and then iterate with for by selecting the output with the if.

t = [-1:0.1:5];

% (a): The Unit-step Function u(t)
function u = u (t)
    u = zeros(size(t));
    for i=1:length(t)
        if(t(i) >= 0)
            u(i) = 1;
        else
            u(i) = 0;
        end
    end
end
plot(t, u(t));

Second solution:

Another solution is to use the properties of matlab/octave to handle vector operations.

t = [-1:0.1:5];

% (a): The Unit-step Function u(t)
function u = u (t)
    u = t>=0
end
plot(t, u(t));

edited Jun 7, 2017 at 1:45

answered Jun 7, 2017 at 1:42

eyllanesc

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1 Comment

nbstrong Over a year ago

Thank you! That makes perfect sense. Also, the second solution is very clever.

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