function kernelMatrix = linearKernel(X1, X2, kernelParams)
%A function to compute the linear kernel matrix entries between X1 and X2.
%These matrices must have the same number of colums 

useSparse = issparse(X1); 
numX1Examples = size(X1, 1); 
numX2Examples = size(X2, 1); 

if useSparse 
    kernelMatrix = sparse(numX1Examples, numX2Examples); 
else 
    kernelMatrix = zeros(numX1Examples, numX2Examples); 
end
    
kernelMatrix = X1*X2';