Triangular and other step functions in matlab

Question

As the title indicates, I need help on how to plot a triangular function in Matlab. e.g.

$ f(x)=\begin{cases} 1-|x|, & |x|< 0 \\ \\ 0, & \text{otherwise} \end{cases}$

As well as the functions

$ Af(x)=\begin{cases} A & x\geq 0 \\ \\ 0 & x<0 \end{cases}$ and $ -f(x)=\begin{cases} -1 & x\geq 0 \\ \\ 0 & x<0 \end{cases}$

I tried and plotted the unit step function

$ f(x)=\begin{cases} 0 & x< 0 \\ \\ 1 & x\geq0 \end{cases}$

as

x=-50:50;
y=[zeros(1,50) ones(1,51)];
plot(x,y);
axis([-55 55 -0.2 1.3])

Thanks for your interest.

Answer 1

Generally, to plot a function you 1) sample the domain, defining a vector x; 2) compute the images of those samples, obtaining a vector y; and 3) use plot(x,y) or similar.

When your desired function graph is composed of straight lines, to get a perfect graph you should choose the sample points as the "corners" of the graph. For example, for the triangular function you should use points with -1, 0, 1 plus some points further to the left and to the right:

x = [-3 -1 0 1 3];
y = [ 0  0 1 0 0];
plot(x,y)
axis([-4 4 -.2 1.2])

If the point has a jump discontinuity you should duplicate the corresponding x in order to get the jump properly. For example, for the step function you could do

x = [-3 0 0 3];
y = [ 0 0 1 1];
plot(x,y)
axis([-4 4 -.2 1.2])