Re: Problem plotting time on X axis

[Przemek Klosowski]

On 02/14/2018 03:08 PM, Fritz Sonnichsen wrote:
> On 2/14/2018 2:25 PM, Przemek Klosowski wrote:
> > On 02/14/2018 02:00 PM, Fritz Sonnichsen wrote:
> > > ser_date=datenum(dtmeT,timeFormat); %serial date is secs since 1/1/0000
> > >   plot(ser_date,T ,'color','k'  );
> > >   datetick('x',timeFormat,'keepticks')
> > >   xlen = length(dtmeT)  ;
> > >   axis([0 xlen 20 35]) 
> >
> > I think it's a manifestation of the magnitude bug in the default 
> > toolkit (fltk?). The problem is that fltk can't plot intervals that 
> > have a short span compared to the magnitude of the endpoints. Since 
> > you don't seem to care about the actual date, resetting the beginning 
> > to midnight works around that:
> >
> > plot(ser_date-datenum("00:00:00"),T ,'color','k' ) 
> I tried that and it did not work.  My "ser_date" is numbers like: 
> 7.3706e+005

Right--you have to do the  whole thing of course, including setting the 
datetick.

dtmeT = {"9:00:38" "9:00:39" "9:00:40" "9:00:41"}
T = [   23.900    23.900   22.900   21.100]
timeFormat='HH:MM:SS';
  ser_date=datenum(dtmeT,timeFormat); %serial date is secs since 1/1/0000
plot(ser_date-datenum("00:00:00"),T ,'color','k' )
datetick('x',timeFormat,'keepticks')

In general, it's  easier for everyone if you ask questions by providing 
a complete, standalone example that can run in a fresh Octave session. I 
just copied-and-pasted the above snippet and got an expected 
graph---what exactly is happening in your case?