Check for missing argument or incorrect argument data type in call to function 'fit' - using two 1x15 double arrays as an input argument

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Laura Stokbro
Laura Stokbro on 7 Sep 2020
Commented: JP on 22 Nov 2020
I am trying to fit to arrays and I get the error 'Check for missing argument or incorrect argument data type in call to function 'fit''.
The code I use:
clear all
close all
clc
year=[1991,1994,1995,1996,1997,2000,2001:1:2004,2007,2008,2016,2021,2024]
capacity=[ 0.4,0.5,0.5,0.7,0.6,2,2,2,3,4.5,5,5,10,12,14]
matrix=[year;capacity]
f=fit(year,capacity,'poly2')
Can anyone tell me what is wrong with this code?
  3 Comments
Laura Stokbro
Laura Stokbro on 7 Sep 2020
Thanks.
Though Ill have to predict future scenarios, so if the development is exponential it will grow faster than predictions using the polynomial fit. So I'd really like to be able to fit the points exponentially as well. Can you help me with that?

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Accepted Answer

Bernard Beitz
Bernard Beitz on 30 Sep 2020
Edited: Bernard Beitz on 30 Sep 2020
Summary: Don't forget to install all needed toolboxes (curve fitting toolbox) after installing a newer version of matlab.
The Problem sounds like you have the statistics toolbox installed but not the curve fitting toolbox. Try typing
which fit -all
to validate. The command will show every function called 'fit' that matlab knows about The correct feedback is similar to this:
>> which fit -all
/MATLAB/toolbox/curvefit/curvefit/fit.m
/MATLAB/toolbox/stats/stats/@gmdistribution/fit.m % gmdistribution method
If fit from curve fitting toolbox is missing, matlab will call the stats toolbox function which has different input types. If both are installed, matlab will determine by the type of the input paramters which function to call, so this won't be a problem.

More Answers (2)

Alan Stevens
Alan Stevens on 7 Sep 2020
Here's a way of fitting a simple exponential curve. However, you definitely don't want to use it to extrapolate!
year=[1991,1994,1995,1996,1997,2000,2001:1:2004,2007,2008,2016,2021,2024];
capacity=[ 0.4,0.5,0.5,0.7,0.6,2,2,2,3,4.5,5,5,10,12,14];
% Exponential fit by taking logs first
% capacity = a*exp(b*year)
% ln(capacity) = ln(a) + b*year
lcap = log(capacity);
c = polyfit(year,lcap,1);
a = exp(c(2)); b = c(1);
capfit = @(t) a*exp(b*t);
t = 1991:2024;
plot(year,capacity,'o',t,capfit(t))
grid
xlabel('year'),ylabel('capacity')
legend('data','exponential fit')

JP
JP on 11 Sep 2020
I get the same error even with the examples from the Help Center: https://de.mathworks.com/help/curvefit/fit.html#bto2vuv-1-fitType
I tried for example this:
load census;
f=fit(cdate,pop,'poly1');
plot(f,cdate,pop)
Is there a problem with fit function in Matlab 2020a?
Best

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