incorrect dimensions for matrix multiplication in piecewise function in matlab

This is what I am trying to implement in Matlab:

where vi = sin(2*pi*1000*t) and VD = 0.72

These are my commands:

>>t = 1:1000

>>t/1000

>>vi = sin(2*pi*1000*t)

>>vo = piecewise(vi<0.72, 0, vi>0.72, (vi-0.72)*exp(-t))

However, I get this error:

Error using * Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

I have no idea what I am doing wrong, any help?

Answer 1

[Torsten]

tau = 1.0;
V_D = 0.72;
vi = @(t) sin(2*pi*t);
f = @(t) max(vi(t)-V_D,0).*exp(-t/tau);
t = 0:0.01:2*pi;
plot(t,f(t))