MATLAB: 4×1 vector to 2×1 vector with S function

s-functionsimulink

Hi,
I have written an Level-2 S-function which creates a 2×1 vector from a 4×1 vector, that it, taking out the first 2 elements.
The function “Output()” is:
function Output(block)
block.OutputPort(1).Data = block.InputPort(1).Data(1:2);
 Error: Attempt to assign a matrix of dimentions [2x1] to a matrix of
 dimensions [4x1].
So I added the following code to the function “Setup()”:
function Setup(block) 
block.OutputPort(1).Dimensions = [2,1];
This time the error is:
 Invalid dimentsion has been specified for input port 1 of …
Now I am helpless with this problem. Who can help me with this problem?
Thanks Senmeis

Best Answer

Hi,
The reason the error is cropping up is because, while the Output Port Dimensions have been explicitly specified, the S-function is relying on implicit inheritance to determine the dimensions of the Input Port. Due to the differing sizes, there's a conflict. By specifying the InputPort dimensions in this way in the setup method:
block.InputPort(1).Dimensions = 4;
you would be explicitly specifying the Input Port dimensions and the S-function should run fine.
Related Question