MATLAB Answers

## Why do I get NaN values?

Asked by Stelios Fanourakis

### Stelios Fanourakis (view profile)

on 22 Apr 2019
Latest activity Commented on by Walter Roberson

### Walter Roberson (view profile)

on 24 Apr 2019
I have used exactly the same code for Sheet 5 and different column names and I get numerical values but when I use it at Sheet 6 and slightly adjacent columns but the same number of rows I get NaN.
Any idea why this happens?
x1 = readtable('ValidationTest.xls', 'Sheet',6, 'Range','N2:N385 ');
y1 = readtable('ValidationTest.xls', 'Sheet',6, 'Range','A2:A385 ');
x2 = readtable('ValidationTest.xls', 'Sheet',6, 'Range','O2:O868');
y2 = readtable('ValidationTest.xls', 'Sheet',6, 'Range','B2:B868');
P1 = polyfit(x1{:,:}, y1{:,:}, 6 )
P2 = polyfit(x2{:,:}, y2{:,:}, 6)
allX = unique([x1{:,:}; x2{:,:}]);
Pd = polyval(P1, allX) - polyval(P2, allX)
P11 = polyval(P1, allX)
P22 = polyval(P2, allX)
hold on
plot(allX, Pd, 'b')
plot(allX, P11, 'g')
plot(allX, P22, 'r')

John D'Errico

### John D'Errico (view profile)

on 24 Apr 2019
The file you attached has only one page in it. If I extract those 4 variables, it appears that y2 is constant at 4.8. ABSOLUTELY constant.
If I plot x1 and y1, I see this discreet mess:
That is what this is all about? An absolutely copnstant function, and a that mess?
Sorry, but how do you justify fitting a 6th degree poltynomial to that? You have asked how many questions on this so far?
Stelios Fanourakis

### Stelios Fanourakis (view profile)

on 24 Apr 2019
@John
The graph is correct. It should be like this more or less. By luck, I sent you one dataset with a constant value. Not all sheets are the same. It’s just happened for the particular one. Most of the datasets are curves.
Hopefully, I need to ask as many questions as I need in order to get the right answer. Hope it won’t bother.
Walter Roberson

### Walter Roberson (view profile)

on 24 Apr 2019
That code is not set up to read the VTest.xlsx file you provided.
The earlier code was set up to read it (once the file name was changed), but it did not take into account that two of the columns were shorter than the others.

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