Hallo, i would like o ask you one question. I have a little question from this theard https://www.physicsforums.com/showthread.php?t=134657 i have a model in matlab and i am using discrete transfer fcn. it using z-transfor with this form 1/z-1 . at input are numbers and at output is one number that is a simple sum of inputs..for example inputs are 1, 2 , 3 and the output of this function is 6 .. everything is fine but i dont know how this fcn calculate it. i think the sequence will be like this: 1*1^(-1) + 2*1^(-2) + 3*1^(-3) = 6 but im not sure its correct. can by the "z"=1? or what exactly is this "z" mean in this formula or in the sum. thank you very much. i hope its easy but i realy wondering about it a lot.