subtract two parameters with diff dimension

i want to subtract two parameters x and y.X has dimension 100* 784, Y has dimension 784*784.Can anybody help

[Walter Roberson]

If you have a particular position (J,K) in the output matrix, how would you calculate the value for that location?

OutMatrix(J,K) = ???

Answer 1

[Azzi Abdelmalek]

The size of Y is greater then the size of X, we can subtract the first 100 rows, but what about the remaining rows in Y? Look at this example, maybe this is what you want, if not, give more details

Y=rand(784);
X=rand(100,784);
Z=[X;zeros(784-100,784)]; % to make Y and X the same size
out=Y-Z;