Function inside for loop not working

Hi, I am trying to iterate the diagonal filling of a previously defined, 0 valued hypercube object with a for loop of the following form:   EDIT - REMAINING CODE:   % Load and adjust test image, convert to .png (probably unnecessary) addpath('D:\Users\Peter\Desktop\Masterarbeit\Messdaten\Bilder_Einfach'); img = imread('BspBild_1.jpg'); imwrite(img, 'BspBild.png'); img = double(rgb2gray(imread('BspBild.png'))); img = rescale(img); sz = size(img); % Create empty hypercube zerocube = zeros(detformat_y, 2*detformat_x, n_lambda); hcube = hypercube(zerocube, wavelengths); % Add image to the first band hcube = assignData(hcube, 1:411, detformat_x/2+1:640+detformat_x/2, 1, img); % Show image as first hypercube band (for testing reasons) figure(2) imshow(hcube.DataCube(:, :, 1)) title('Cube-Ausschnitt') % loop to "shear" image in the wavelength direction EDIT - END for k = 1:n_lambda % n_lambda is the number of bands temp = img(:, k); % img is the monochromatic image that should fill a diagonal line hcube = assignData(hcube, :, k, k, temp); end the function assignData is defined in the Image Processing Toolbox Hyperspectral Imaging Library and works fine outside the for loop.   Whenever I try to execute the code it gives me "Unrecognized function or variable 'assignData'." in the line with this function.   Since directly indexing inside the hcube.DataCube object is not possible this function seems to be the only option to change hyperspectral data.