It seems that you have opened the file for writing ('w') which erases the exisitng file, if it exists. You write the time vector to the file. Then you attempt to read from the file with fscanf(). You would have to close it first, the open it for reading ('r'). I'm not sure exactly what you are trying to do. If the text file already exists, with 2 columns of data (time and the sine wave), then do
data=load('sine50Hz.txt','-ascii');
plot(data(:,1),data(:,2))
If the text file is just 1 column of data, the sine wave without the times, the do the following:
sine50=load('sine50Hz.txt','-ascii');
Fs=10e3; dt=1/Fs;
t=(0:length(sine50)-1)*dt;
plot(t,sine50)
Try it. Good luck.
