TF function on Simulink

Hello I am trying to create a MATLAB function on simulink that ,between others, requires the use of the 'tf' function . Problem is I can't really find a way to use the output of the 'tf' function since it's an mxarray. So when I run something like this

function y = fcn(u)
%#codegen
coder.extrinsic('tf')
g=tf([1],[1 1]);
y=0;
y=g*u;

I get this error: MATLAB expression 'mtimes' is not numeric. Block MATLAB Function (#36) While executing: none . Initializing g gives me the 'is not numeric' error so it won't help... So I was wondering if there is anyway to get it done - the scripting way, I know I can use transfer function simulink blocks etc...Thanks in advance. (I am using Matlab R2012b btw)

[Azzi Abdelmalek]

What do you want to do?

[Manos]

I want to get a transfer function from a simulink matlab function using 'tf' like in the code I quoted .

[Manos]

What I am asking is : If there wasn't a "Transfer Function" block on Simulink already , how would you "design" it manually using a matlab function block?

[Ryan Rizzo]

Hi Manos, how did you manage to solve this issue?

Answer 1

[Rick Rosson]

Multiplication is not the same thing as convolution. This approach will not work. You need to write a function that performs continuous time convolution. The only way to do that is to approximate the solution by approximating the continuous integral as a discrete summation over a small sample size. It should be possible, but not easy or fun.

Why not just use the TF block provided by a Simulink? No sense reinventing the wheel.

[Manos]

But since G is in the frequency domain isn't multiplication correct? Why would I have to use convolution??? (I know it makes absolutely no sense trying this the long way, I am just really stubborn :P ) Thanks a lot for your answer Rick!