In Matlab how to generate some random number which satisfies some constrains

how to generate the matrix of random numbers in Matlab which satisfies some constraints? eg. If I want to generate a matrix of 20 by 12 order such that 1 row represents the 12 random numbers that satisfy sum of first four numbers is less than some number and sum of next four number is less than some other number and sum of the first third and fifth number is greater than some number?