Not enough input arguments. What does that mean?

function [I,labels,i_test,labels_test] = readmnist (num)

Path = './testmnist/mnist/train-images.idx3-ubyte ';
if (~exist (path, ' file '))
Error (' Training set of MNIST not found. Download it from Http://yann.lecun.com/exdb/mnist/and put to./testmnist/mnist folder ');
End
FID = fopen (path, ' R ', ' B '); %r is a reading read-only Big-endian high byte order is the upper byte emitted at the low address end of the memory, the low byte is discharged at the high address end of the memory
Magicnum = fread (fid,1, ' Int32 '); %1 is read as a variable Magic number ' int32 ' Integer (integer), + bits.
if (magicnum~=2051)%~= is not equal to the meaning
Display (' Error:cant find magic number ');
Return
End
Imgnum = fread (fid,1, ' Int32 '); %number of images
Rowsz = fread (fid,1, ' Int32 '); %image height
COLSZ = fread (fid,1, ' Int32 '); %image width

if (numImgnum=num;
End

Error using Readmnist_image (line 19) has occurred
Not enough input arguments. What does that mean?

Help.