MATLAB: Help! plotting i(t) vs t.

help! plotting i(t) vs t.homework

Hello, i got stocked bulding my code for this problem.
      a) plot i(t) vs. t, over -pi<t<3pi. 
      i(t)= {3+5*sin(2*t-pi)+t*exp(-t)}[u(t)-u(t-2*pi)]
      b) determine the values for i(t) for t = 0, pi/2, pi and -pi/2
      c) evaluate RMS value of i(t)
This is what I have so far:
      % Script file : sym _ analysis _ RLC
      % Analysis of an RLC series circuit
      % where the current is iamps i(t)= {3+5*sin(2*t-pi)+t*exp(-t)}[u(t)-u(t-2*pi)]
      % R=2K Ohms, L=3mH, and C=1 microF
      function i(t) = ?????
      u = double(t>=0);
      echo off;
      iamps= {3+5*sin(2*t-pi)+t*exp(-t)}*(u(t)-u(t-2*pi));
      figure(1)
      subplot(2,2,1)
      ezplot(iamps)
      title('i(t) vs.t');
      ylabel('Amplitude (amps)');
      grid on
ALL advice will be really appreciated.
Thanks.

Best Answer

You cannot list a subscripted variable on the "function" line of a definition.
function iamps = i(t)
You also need to change the {} to ()
iamps = (3+5*sin(2*t-pi)+t*exp(-t))*(u(t)-u(t-2*pi));  %{} became ()
If you are planning to pass a vector of t in, then you need to convert the * into .* in order to vectorize-- In MATLAB, * is algebraic matrix multiplication, not element-by-element multiplication.
   iamps = (3+5*sin(2*t-pi)+t.*exp(-t)).*(u(t)-u(t-2*pi));  %vectorize as well
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