Plotting two function in one figure

calculate y(t) for the following equation:

y(t) = -2*t^3+5 (t>=0) and y(t) = 2*t^3+5 (t<0).

The values of y should be calculated in the range -9 <= t <= 9. Calculate
a value of y for every t in increments of 0.1 in the range specified. The
values of y should be collected in a single array. Generate a plot of y vs. 
t using the plot command. The curve should be in solid green line with width
of 2. Make sure you have proper axis labels.

This is what I've come up too:

t = [ -9 : 0.1 : 9 ];
for ii = t >= 0
    y = -2*t.^(3)+5;
end
for jj = t<0
    y = 2*t.^(3)+5;
end

plot(y , 'g', 'linewidth',2)

I'm wondering shouldn't my x axis be the t values, I think I've got something missing here.

Answer 1

[Ingrid]

you are not storing your values in a vector y since therefor you would need to indicate y(ii). Also the for command will not be working, instead you need to use a logical indexing

t = [ -9 : 0.1 : 9 ];
y(t>=0) = -2*t(t>=0).^(3)+5;
y(t<0) = 2*t(t<0).^(3)+5;
plot(t,y , 'g', 'linewidth',2)