Help! plotting i(t) vs t.

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.

[Stephen23]

The first and most important advice is to format your code! In its current form it is unreadable. Please edit your question, select the code-text and then press the {} Code button above textbox. Simple!

Or, if you want to do it by hand, just put two-spaces at the start of each code line.

More markup info here: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[David Perez Ramos]

Sorry did not realize how it was written on the preview. it is readable now.

thanks.

Answer 1

[Walter Roberson]

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

[Walter Roberson]

 u = @(t) double(t>=0);

[David Perez Ramos]

Thanks for the help. I did what you said. But how to h define U(t)? Use Heaviside?

[David Perez Ramos]

Thank you. I will try it now.