Calculate slope at specific time over many days using polyfit and for loop

I have a data set that show daily fluctuation in groundwater. I need to find the slope of the hydrograph every day between the hours of 4 and 12. I have tested this loop with other operators and they are working on the correct intervals. the hours 12 to 4 correspond to the first 17 rows of every 96 rows.

How do I correctly use polyfit to calculate slope during the assigned intervals?

The error I am recieving is as follows:

Unable to perform assignment because the indices on the left side are not compatible with the size of

the right side.

Error in ETg_toy (line 105)

tR(h)=polyfit(subset_day,subset_depth,1)

Below is the code I am trying to use:

load('GroundwaterDataA');

A = GroundwaterDataA;

depth=flip(A(:,2))

day=flip(A(:,1))

for h=1:200 %day day 200 = day 199

start2=(h*96)-15;

endp2=h*96;

subset_depth=depth(start2:endp2)

subset_day=day(start2:endp2)

tR(h)=polyfit(subset_day,subset_depth,1)

pause

end

Answer 1

[Star Strider]

You appear to be calculating them correctly, just not storing them correctly. For a linear fit, polyfit will produce a (1x2) vector of the coefficients.

Try this:

tR(h,:)=polyfit(subset_day,subset_depth,1)

Note the added dimension.

[Benjamin Downing]

That solved the issue. Thank you for your help!

[Star Strider]

As always, my pleasure!