Indexing error message that makes no sense with cfit

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Kate 2018-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/399246-indexing-error-message-that-makes-no-sense-with-cfit

评论： Star Strider 2018-5-5

Hi y'all,

I'm trying to fit a polynomial to some data, and I keep on getting an indexing error message which makes no sense. Perhaps one of you can see the forest for the trees. Here's an example of the data:

r =
6406    2.8430
8598    1.9837
8369    1.2979
8227    1.0700
3950    1.8485
8152    2.5149
3562    4.4245
5249    2.7839
0158    1.6553
3364    3.1090
7304    2.3873
4503    1.3488
8857    1.9761
4438    8.2376
5644    7.2797
6695    4.7655
3061    1.9693
2177    3.8884
6174    2.3952
3180    8.7369
6436    5.7631
   -4.3673    1.1343
9130    0.5210
9632    6.3485
6363    4.9399
4421    3.3374

but when I try and fit it I get an indexing error message which makes no sense:

f=fit(r(:, 1), r(:, 2),'poly2')
Subscript indices must either be real positive integers or logicals.

I don't see how this can be an indexing issue, as I can index to plot the full dataset:

figure, plot(r(:, 1), r(:, 2), '.')

Any ideas? I've even re-started matlab as it does sometimes get buggy when I've had it open for a while, but no dice.

Thanks!

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Answer 1

Star Strider 2018-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/399246-indexing-error-message-that-makes-no-sense-with-cfit#answer_318846

在 MATLAB Online 中打开

My guess is that the error refers to fit, and MATLAB believes it’s an array, not a function. Do you have a previously assigned variable named ‘fit’ that’s ‘overshadowing’ the function name?

Run this from your Command Window or a script:

which fit -all

If the first line in the returned output is:

fit is a variable.

You’ve found the problem. The solution is to name the variable something else.