Vector size error or Polyfit

Am trying to detrend some ECG data using polyfit(). Error message is that X and Y vectors not the same size. But they are, I think:

Workspace:

ChannelFirst 1x92672 double t 92672x1 double

Here’s the code:

t = (1:length(ChannelFirst))';

subplot(2,1,1) plot(t,ChannelFirst), grid title 'ECG Signals with Trends', ylabel 'Voltage (mV)'

subplot(2,1,2) plot(t,ChannelFirst), grid xlabel Sample, ylabel 'Voltage (mV)'

Code works fine to this point. Plot looks correct. However,

 opol = 6;
[p,s,mu] = polyfit(t,ChannelFirst,opol);

Error using polyfit (line 47) X and Y vectors must be the same size.

t and ChannelFirst appear to be the same size

can someone please help ? are t and Channelfirst not the X and Y vectors for polyfit?

Answer 1

[Walter Roberson]

[p,s,mu] = polyfit(t.',ChannelFirst,opol);

or

[p,s,mu] = polyfit(t,ChannelFirst.',opol);

One of your vectors is a row vector and the other is a column vector. You need to have them the same orientation.

[Don]

Thank you very much. I could not find that clue in Polyfit() documentation, so took the tutorial code a face value (t' used there) When changed to t it works like a charm. Karma!