Array indices must be positive integers or logical values.

I am trying to plot a v-t graph which pwm(t, T, d) wil be set to 1 if kT ≤ t < (k + d)T and to 0 if (k + d)T ≤ t < (k + 1)T. The below is my script:

T = 2*pi;
d = 0.5;
syms v;
for t = [0:1:10]
    v(t) = pwmmode (t,T,d);
end
plot (t,v);
function y = pwmmode (t,T,d)
   k = 1;
   if ((k*T <= t) & (t <= (k+d)*T)) y =1;
    elseif (((k+d)*T <= t) & (t<(k+1)*T)) y=0;
    else y = 2;
end
end

When I run my script above, I receive errors in the window. Below are the errors displayed on my window:

[Stephen23]

for t = [0:1:10]
    v(t) = ...
end

Zero is not a valid index.

Answer 1

[KSSV]

In MATLAB arrays indices cannot be negative/ zeros. Your code:

for t = [0:1:10]
    v(t) = pwmmode (t,T,d);
end

Should be like:

t = 0:1:10 ;
v = zeros(size(t)) ;  % intialize accordingly 
for i = 1:length(t)
    v(i) = pwmmode (t(i),T,d);
end

[Walter Roberson]

Or in this particular case you could abbreviate to

for t = [0:1:10]
    v(t+1) = pwmmode (t,T,d);
end

However, KSSV's suggstion of creating the list of values ahead of time and looping through indices is a more general approach that you should learn how to use. For example if you were to use

for t = [0:1/3:10]
    v(3*t+1) = pwmmode (t,T,d);
end

then you would fail because the t values would not be exact multiples of 1/3