Plot Time Sensitive Data plus a fit in the same plot

Hello,

I imported two column vectors from an Excel sheet. One is called 'Thickness' and the other 'Date', which contains the Date of the measured thickness in the format: 'DD-MMM-YYY HH:MM:SS'.

I now want to achieve two things. To plot the thickness over time with a fit, and have the x-Axis displayed in the time format DD-MMM-YYY. I have no trouble with the plot, simply

plot(Date,Thickness,'.')

works fine. Then, i want to apply a general fit to the data, to see the overall tendency of thickness over the last year. I used

fit1 = fit(DateTime,Thickness,'poly1');

to create the fitted line. 'DateTime' is the Date vector, converted with

datenum(Date)

since the fit-function does not accept datetime variables. But the big problem is: How do I plot the fit and the thickness in one plot, AND let the x-axis be displayed in DD-MMM-YYYY? The plot won't work if the fit and the data have different types. Fit in 'datenum', Date in 'Datetime', aparrently can't be plotted simultaneously. I've tried hold on/off, with no luck.

It is possible to also convert the Date into datenum, but then the x-axis labels don't help in finding correct dates.

Thanks in advance!

Answer 1

[Yongjian Feng]

To show more than one plots in a figure, use

plot(Date, Thickness, '.');
hold on % this means you want more than one plots in a figure
% plot the fit here

hold off

[Tim Richter]

If I do it like this:

plot(Date,Thickness,'.');

hold on

plot(fit1,'-r') % or plot(Date,fit1,'-r') or plot(DateTime,fit1,'-r')

hold off

I get the error: 'Error evaluating CFIT function - Arguments must be numeric, char, or logical.'