Is this correct?

Use loops to compute and plot (not animated)the following piecewise function for -15<=x<=15 .

F(x)={5x, x<0

{x^2, 0<=x<2

{ 2lnx, x>=2

My code:

x=-15:15; 
    if x<0;
        5*x;
elseif x>=0 & x<2
    y=x^2;
    else x>=2;
    y=2*log(x);
end 
plot(x,y)

Warning: Imaginary parts of complex X and/or Y arguments ignored.

[Matt J]

Clearly it is not correct. You can see that your code produces an error message.

[Allison Sims]

Okat what about now

[M.B]

Check your variable names and indexation.

[Chunru]

Although the code is not doing what it intends to, the code can be run and MATLAB only gives a warning message (orange color).

Answer 1

[Chunru]

x=-15:15; 
y = zeros(size(x));

% This is more MATLAB way
idx = x<0;      
y(idx) = 5 * x(idx);

idx = x>=0 & x<2;
y(idx) =x(idx).^2;

idx = x>=2;
y(idx) = 2*log(x(idx));

plot(x,y)

% This is more conventional way (some othter programming language)
x=-15:15; 
y = zeros(size(x));

for i=1:length(x)
    if x(i)<0
        y(i) = 5 * x(i);
    elseif x(i)>=0 & x(i)<2
        y(i) =x(i).^2;
    elseif x(i)>=2;
        y(i) = 2*log(x(i));
    end
end
figure
plot(x,y)

[Allison Sims]

That makes more sense thank you!

Answer 2

[M.B]

x = -15:1:15;% init x
y = nan*x;% init y to be of same size as x
for index = -15:15; 
    if index<0;
        y(index+16) = 5*index;
    elseif index>=0 & index<2
        y(index+16) = index^2;
    else index>=2;
        y(index+16) = 2*log(index);
    end 
end 
plot(x,y)

[Allison Sims]

what does the y(index+16) mean?

[Chunru]

The "index" is the loop variable the code uses and it need to be added with 16 in order to become array index (which is 1,2,...31). It's working code, but it may be further improved.