Index in position 1 is invalid. Array indices must be positive integers or logical values?

why am getting this error?

the error massage is:

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in secondparameterestimation (line 109)
Ppost= (1./((2*pi*sigma.^2)^(N./2))).*exp(-sum(I,2)./(2*sigma.^2));

Here is the main code:

N=12;
sigma=100;
Ymeasurement=[347.6192  349.8622  350.5189  351.6964  352.6208  358.4055  356.9439  358.2743  352.8084  350.9066  347.9320  349.0564];
I=zeros(1000,12);
pi=3.1415926;
for i=1:1000
    for k=1:12
        I(i,k)=(Ymeasurement(1,k)-(T{i}(k))).^2;
    end
end
Ppost= (1./((2*pi*sigma.^2)^(N./2))).*exp(-sum(I,2)./(2*sigma.^2));
Pmax=max(Ppost);
l=Ppost./Pmax;

    plot(ri,l,'r.')

[KSSV]

What is T?

[Deepesh Kumar Gupta]

T is the Temperature ,which has been taken from the previous code

[Cris LaPierre]

Run the following code in your command window and share the result.

which sum

[Deepesh Kumar Gupta]

Thank you @Cris LaPierre, the problem has been resolved.Thanks for your efforts.