Port width missmatch for Matlab Function Block in Simulink

Hello everyone,

I am using a Matlab Function block in a Simulink model and I set the input data type in the Ports and Data Manager to "Inherit". The signal arriving at the input port is called "history" and of the size [10x3]. When I try to run the model I get the error:

"Port width mismatch. Input 'history' expects a signal of size [10xx3]. The signal received is of size [10x3]."

Now I know [10x3] means a matrix of the size 10 by 3, but what does [10xx3] mean and why does the program ask for that format?

I'm thankful for any kind of help.

Cheers,

Manuel