Huge Execution Time Discrepancy with line() Command

The following code takes no more than 4 seconds to execute:

figure(statfig);
set(gcf,'Position',get(0,'ScreenSize').*[1 1 0.5 1]);
titlestr = [test ' - Statistics - ' num2str(rpmval) 'RPM - ' samplestr ' - ' upper(sensor)];
subplot(size(detdata,2),1,var);
plot(detdata(:,var)');
hold on;
% line([1:length(detdata)],avg_env_sample(var),'Color','r');
% line([1:length(detdata)],avg_env(var),'Color','g');
hold off;
% legend('Detrended Data','Envelope','Envelope Mean');
title([titlestr ' - ' varname]);
xlabel('Sample [n]');
ylabel([varname ' [g]']);
set(gcf,'Name',titlestr);

With the commented code uncommented, execution time goes up to two minutes. Similar code is executed 3 other times (without the line commands) without a problem.

Any suggestions?

[Walter Roberson]

Could you give us an idea of length(detdata) ?

[Eric]

16000

[Eric]

But plot() gets executed on that sized data many (hundreds) of times, with no issues.

Answer 1

[Rob Graessle]

Are you expecting each call to 'line' to draw 15999 lines or just one line? If it is the latter, try this instead:

line([1 length(detdata)],avg_env_sample(var),'Color','r');
line([1 length(detdata)],avg_env(var),'Color','g');

[Walter Roberson]

It appears to me that var is a scalar, as otherwise the subplot() would not work. Then in order to draw a horizontal line, the y coordinate would need to be duplicated:

line([1 length(detdata)],avg_env_sample([var var]),'Color','r');

line([1 length(detdata)],avg_env([var var]),'Color','g');

[Eric]

So my understanding is this will draw a horizontal line interpolated from two (x,y) points instead of a 16000 point line? I still don't understand why the execution of the original code is so slow if plot() executes so quickly on the same sized data. But it does bring everything back to normal. Thank you Walter and Rob.