Plotting basics

[Byron Hawkins]

I’m trying to make some very simple line plots, and I keep getting errors and strange output. My script just takes the matrix “plots” and the vector “index” and does this:

 

if length(plots) > 0,

  semilogy(index, plots);

end;

 

1.       There is a warning about “axis: omitting non-positive data in log plot”. There are zeros in the matrix, but these are not drawn in the plot, which makes it look incomprehensible. Is it a problem to plot zeros? I’m not specifying any axis bounds, so maybe the auto-bounds generator is specifying zero, and that conflicts with the semilogy() function? I need to show zeros, but there needs to be logarithmic scaling too.

2.       All the documentation says that “semilogy” and “plot” work just the same, but when I change “semilogy” to “plot”, I get errors about “subscript indices must either be positive integers less than 2^31…” What does it mean? Why can’t I have a linear plot?

3.       When I use the axis() function, all my inputs are ignored. It just plots the same auto-bounds that it was plotting before. I call it like “axis([1,30,-100,1000]);” before anything else happens in the script.

 

It would be really great if someone could point me in the right direction here, I have a paper deadline coming up very soon and I am totally stuck with this really basic plotting. Thanks for your help.

 

Byron