Plotting a density function I am trying to plot the following function in MATLAB

$$f(x) = \lambda e^{-\lambda(x-\Delta)}w(x-\Delta) $$

where 
$$w(x) = 
         \begin{cases}
           1 &amp;x \geq 0 \\
           0 &amp; {\rm otherwise}\\
         \end{cases}
    $$

I chose a value of $\lambda$ of 1 and $\Delta$ of 2. I am just not sure how to define $w(x)$ and shift the function by delta. Thank you.
You can plot samples of a continuous density function just as you would do with any continuous function. Assuming $w(x)$ represents the continuous-time unit step function,

$$w(x-\Delta) = \begin{cases}{ 1 ~~~,~~~x \geq \Delta \\ 0 ~~~,~~~  \text{otherwise} } \end{cases}$$

then the shifted exponential pdf can be plotted with the following matlab/octave code :

clc; clear all; close all

K1 = -1;        % evaluation interval begins
K2 = 9;         % evaluation interval ends
N = 1000;       % number of points to display
x = linspace(K1,K2, N); % x = domain to use for displaying 


lam = 1;        % exponential PDF parameter
delta = 2;      % shift amount
f = lam*exp(-lam*(x-delta));
f = f.*(x&gt;delta);   % to implement w(x-delta)

figure, plot(x,f);
title('shifted exponential pdf for \lambda = 1, \Delta = 2');


The output will be: