general comments to make to class:

there are two types of general issues:

1. nontechnical.

**i'm tired--write clearly!

**from now on, state who created figure for each figure used.

**in ps_ch, use /defaults keyword. mistake in idl tutorial forgot it.

**figure captions: generrally not enough info! self-contained.

techncal in a fundamental sense:

strict equality and fidelity of ft's, even with only 2.1 points per
period. CDs as e.g.

why is the fsig=0.5 fsmpl sig showing only at negative freqs?
 --this ties into:
extreme nyquist violation. explain 50 kHz smpl freq with 5.01 MHz
signal.  

use fft from now on
fft is a function. write the sum that it's evaluating, show how delta f
and delta t cancel out.
**negative limits in eqn discrete version of analytic ft
describe how fft works and why it's faster
describe the output