Error using reshape syntax

I'm new in Matlab. I want to reduce the size of the vector magnitude to smaller so that later I can use it for the KNN classification. So I try use 'reshape' to reduce the vector column size to 100

Error using reshape
To RESHAPE the number of elements must not change.

Error in Gabor2 (line 25)
    rs = reshape(mag,1,250*250);

Here is my code..

%Pelatihan (Training)
folder_citra = 'data latih';
nama_citra = dir(fullfile(folder_citra, '*.jpg'));
jumlah_citra = numel(nama_citra);

for n = 1:jumlah_citra
    % Membaca citra
    Img = imread(fullfile(folder_citra, nama_citra(n).name));
    % Resize citra
    Img_resize = imresize(Img, [250 250]);
    % Konversi citra RGB menjadi Grayscale
    Img_gray = rgb2gray(Img_resize);
    
    % Ekstraksi Ciri Tekstur Filter Gabor
    wavelength = 4;
    orientation = 90;
    [mag,phase] = imgaborfilt(gray, wavelength, orientation);
    rs = reshape(mag,1,250*250);
    mag_kecil = imresize(mag,1/25);
    training = reshape(mag_kecil,1,100);
end

Answer 1

[Walter Roberson]

reshape() can never be used to make an array smaller. It can only be used to change how a block of memory is indexed, with the number of elements having to stay the same.

You might be able to use resample() for your purposes.