if statement for piecewise function

I have a piecewise function like :

p(t) = ( 0.30*beta 0<t<10 s 
-0.30*beta 10<t<20 s
0               t<20 s   ) 

i write this on matlab like this:

if t>0,t<10;
    p(t)=0.30*beta; 
elseif t>10,t<20; 
    p(t)=-0.30*beta; 
else
    p(t)=0;
end 

and i got an error like this " Not enough input arguments." so what am i doing wrong? can you help me?

Answer 1

[Walter Roberson]

p = zeros(size(t));
for K = 1 : numel(t)
    if t(K)>0 && t(K)<10
        p(K)=0.30*beta; 
    elseif t(K)>10 && t(K)<20 
        p(K)=-0.30*beta; 
    else
        p(K)=0;
    end 
end

Notice that if you are going to use if statements and t is a vector, then you need to loop over all of the entries in the vector.

However, in many cases, it is better to use logical indexing instead of looping.

p = zeros(size(t));
mask = t > 0 & t < 10;
p(mask) = 0.30*beta;
mask = t > 10 & t < 20;
p(mask) = -0.30*beta;

No need for an else because all elements were initialized to 0 anyhow.

Caution: when t = 10 exactly your code falls through to the else and assigns 0 there.

Caution: your code does not implement the same as the function definition. The function definition does not define any value for complex-valued t or for t >= 20, but your code would assign 0 to those locations. When a function definition does not define a result for a case, the code should either error or generate NaN if that situation is encountered.