Well, I want to show that a function is a valid kernel function . The function is,

$ $ k(x,z)=\min(x,z)$ $

Thus, I formed a $ N\times N$ Kernel (Gram) matrix,

$ $ K=[k(x_i,x_j)]$ $

for a data set $ x_i$ , $ i=[1:N]$

How do I show that this matrix is Positive Semi-definite Page 4 of the pdf?