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Re: Plotting basics
From: |
Ben Abbott |
Subject: |
Re: Plotting basics |
Date: |
Fri, 21 Feb 2014 03:39:00 -0500 |
On Feb 21, 2014, at 3:27 AM, Byron Hawkins <address@hidden> wrote:
> 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.
The log of zero is -infinity. How would you like to illustrate that in your
plot?
> 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?
The error indicates you are indexing an array with negative values and/or with
values larger than 2^31. For example ...
x = rand (10,1);
n = 2e50;
x(n)
error: subscript indices must be either positive integers or logicals
n = -1;
x(n)
error: subscript indices must be either positive integers or logicals
> 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.
To make axis ([...]) apply to future commands, you need to add "hold on". Try
...
axis([1,30,-100,1000]);
hold on
... and then add your plot commands.
>
> 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
- Plotting basics, Byron Hawkins, 2014/02/21
- Re: Plotting basics,
Ben Abbott <=
- Message not available
- Re: Plotting basics, Ben Abbott, 2014/02/21
- RE: Plotting basics, Damian Harty, 2014/02/21
- Message not available
- Re: Plotting basics, Ben Abbott, 2014/02/21
- RE: Plotting basics, Byron Hawkins, 2014/02/21
- Re: Plotting basics, Mike Miller, 2014/02/21
- RE: Plotting basics, Byron Hawkins, 2014/02/21
- Re: Plotting basics, Ben Abbott, 2014/02/21
RE: Plotting basics, Damian Harty, 2014/02/21