MATLAB：单位步长函数

Question

For some reason when I try to create a simple unit step function I just receive a straight line. I am pretty sure this is correct, but my graph tells me otherwise. Is there something I am doing wrong?

function mone=myOne(t)

[n,~] = size(t);

mone=zeros(n,1);

for i=1:n,

    if (t(i)>0), 

        mone(i) =  1;

    end
end

in the command window I type,

t = [-5:0.01:5]

plot(t, myOne(t))

Answer 1

The error is your line:

[n,~] = size(t);

You only query the first dimension of t , which is 1 following

t = [-5:0.01:5]
size(t)

ans =

       1        1001

You can either transpose t

t = [-5:0.01:5].';
size(t)

ans =

        1001           1

or you length instead of size .

n = length(t);

Finally, a solution without the loop as proposed by @Dan is much faster.

Answer 2

I can't see anything wrong with the logic behind your function but your implementation is very long winded. In Matlab you can just do this:

function mone=myOne(t)
    mone = t > 0;
end

or if you want to get a matrix of numbers and not logicals returned try

function mone=myOne(t)
    mone = (t > 0)*1;  %// Or if you prefer to cast explicitly:
                       %// double(t>0)
end

Also to add a shift parameter with default set to zero:

function mone=myOne(t, T)

    if nargin < 2
        T = 0;
    end

    mone = (t > T)*1;

end

usage:

t = [-5:0.01:5]
plot(t, myOne(t))
plot(t, myOne(t,3))