Error when adding values to array in loop

I'm trying to add the mean and standard deviation values of a timeseries in a loop to the proper arrays, however i am running into the same error in the multiple ways i'm trying to do it. Here's the code:

    for i=31:30:length(TotalReadingsB)
        MediaMatriz = [MediaMatriz mean(TotalReadingsB(i-30:i))] %Média de cada mês
        SMatriz = [SMatriz std(TotalReadingsB(i-30:i))] %Desvio padrão de cada mês
    end

The series contains data for a year and the objective is to collect the the aboce mentioned valued monthly.

This results in the fallowing error:

    Dimensions of matrices being concatenated are not consistent.

[Walter Roberson]

What size() are MediaMatriz and SMatriz before this loop starts?

[Guilherme Nogueira]

They don't initiate with a set size. The final arrays will have size 12 but i want to add the calculated values at the end so i just initiated them like

MediaMatriz;

[Walter Roberson]

MediaMatriz;

does not initialize: it causes MediaMatriz to be looked up in the symbol table, gives an error if it is not found, then because of the ';' it discards the output of displaying MediaMatriz .

You need an initialization, something like

MediaMatriz = [];

[Guilherme Nogueira]

Yes that works! Thanks!