Problem with getting results for plotting (X,Y)

• Question is:
• X axis (t) = from 0 to 30;
• Y axis (A) = if command; if t>=10 and if not,

Error:

Subscript indices must either be real positive integers or logicals.

Error in SpecifyLineStyleColorAndMarkerExample (line 9)

A(t) = rav * t;

A=ones(1,30);

rav = 0.5;

rln = 0.1;

for t = linspace (0,30,31);

if t<=10

A(t) = rav * t;

else

A(t)= rav*10 + rln * (t-10);

end

end

Answer 1

[DGM]

The index t increments through the integers 0 to 30. While it's true that t is always an integer, it is not a positive integer. For the first pass through the loop, t=0. A has no zeroth element. Matlab uses a 1-based indexing convention, so perhaps:

for t=1:30

would work (provided all the other math works out).

[Armin Majidian]

Thank you

If I put t=1:30 insted of t = linspace (0,30,31), the answer for t is just 30, not 1 to 30 (and not zero).

Please help me through this

A=ones(1,30);

rav = 0.5;

rln = 0.1;

for t = 1:30;

if t<=10

A(t) = rav * t;

else

A(t)= rav*10 + rln * (t-10);

end

end

ANS:

t=

30

[DGM]

Yes. The last value of t is 30. That's what it is in the last pass through the loop.

If you want to generate vectors to plot, t should be a vector not a loop iterator. We can simplify this whole thing:

% define parameters
rav = 0.5;
rln = 0.1;

% define vectors
t=1:30;
A=zeros(size(t));

% do the piecewise math
A(t<=10) = rav*t(t<=10);
A(t>10) = rav*10 + rln*(t(t>10)-10);

% plot A vs t
plot(t,A)

[Armin Majidian]

That was really helpful. Thank you for your guidance,

And now how can I connect the (0,0) to the rest of the plot?

[DGM]

Oh, my bad. In this context, since t is not an index, you can use:

t=0:30;