Need help multiplying matrices of different sizes

I am having trouble multuplying the dtnewnew matrix by the acceleration matrix. Both of them should be vectors but they are vectors of different length. How do I make it so that they are the same length? Please note that the length of the acceleration vector will change since I am picking 50 random files out of 7092 files

Error using reshape

Number of elements must not change. Use [] as one of the size inputs to automatically calculate

the appropriate size for that dimension.

Error in newearthquakes (line 19)

dtnewnewnew=reshape(dtnewnew,size([]));

HERE IS MY CODE:

%IMPORT THE ACCELERATION FILE AND GETTING 50 ACCELERATION FILES
%making loop so it does this 50 times
 
%picking 50 random numbers
 
for i=1:1:50
    a=randi([1,7092]);
    name=['R',num2str(a),'.txt'];
    data=importdata(name);
    acceleration=data(:);
    newacceleration = acceleration(1:3516,:)
    %trouble matching the end of the acceleration array to the 3516 of the
    %excel file
    %IMPORT THE dt FILE from excel
    excelfile = xlsread('Final_NGA_Flatfile.xlsx');
    %TO GET THE X VALUES, MULTUPLY DT BY ACCELERATION VALUES
    dt=['D',num2str(a-1)];
    dtnewnew=dt(:);
    dtnewnewnew=reshape(dtnewnew,size([]));
    xvalues(:,i)=bsxfun(@times,dtnewnew,newacceleration);
 
%PLOT/LABEL
plot=scatter(xvalues,newacceleration,'.');
xlabel('time');
ylabel('acceleration');
title('Earthquake Data (acceleration vs. time)');
end 

[Anish Walia]

Can you upload the data files too? And provide the sizes of acceleration matrix and dtnewnew matrix

[Sofija Radulovic]

the acceleration matrix is changing because it is randomized, i cannot upload the data files because there are 7000 of them, and the dtnewnew matrix is 7094 x 1

[Walter Roberson]

size([]) is [0 0], and reshaping dtnewnew to 0 by 0 will fail unless dtnewnew is already empty.

If dtnewnewnew is intended to be a row vector, then just take dtnewnew.' since dtnewnew is certain to be a column vector.