I am getting error Undefined function or variable, How to solve this error??

I am trying to run this code but I am getting error.

clear;
tic;
DataX = zeros(28709,2304,'single');
DataY = zeros(28709,1,'single');

fid = fopen('train.csv');
C = textscan(fid, '%d', 2305, 'Delimiter', '",', 'Headerlines',1, 'MultipleDelimsAsOne', 1);
DataX(1,:) = C{1}(2:end);
DataY(1) = C{1}(1);
for i = 2:28709
    if mod(i, 1000) == 0
        i;
    end
    C = textscan(fid, '%d', 2305, 'Delimiter', '",', 'MultipleDelimsAsOne', 1);
    DataX(i,:) = C{1}(2:end);
    DataY(i) = C{1}(1);
end
fclose(fid);
toc;
DataX = DataX./255;

im = write_grid_images(DataX, [48 48], [10 10], 2, 1);
myfclf(1); imshow(im);

save data.mat DataX DataY;
tic;
fid = fopen('test.csv');
C = textscan(fid, '%s', 'Delimiter', '" ', 'Headerlines',1, 'MultipleDelimsAsOne', 1);
fclose(fid);
toc;

CC =reshape(C{1}, 2304, 3589*2);

TestX = zeros(2304,3589*2,'single');
for i = 1:2304
    for j = 1:3589*2
        TestX(i,j) = str2double(CC{i,j});
    end
end

TestX = TestX'./255;

im = write_grid_images(TestX, [48 48], [10 10], 2, 1);
myfclf(1); imshow(im);

save test.mat TestX;

This is the error

   Undefined function or variable 'write_grid_images'.

Error in programm (line 22)
im = write_grid_images(DataX, [48 48], [10 10], 2, 1);

Answer 1

[Walter Roberson]

You need to install https://github.com/HamedMP/deep-learning-faces to use write_grid_images()

[saeeda saher]

Now installed write-grid-images() and added it into path file, the error is gone. Thank you

Answer 2

[Christoph F.]

The error means MatLAB cannot find the function write_grid_images().

Is it defined in a separate file or in the same file as the rest of the code?