simulink undefined funciton or variables

I am doing a simulink project of robotic arm and this is my diagram so far.

You see the red color certain blocks, it says unrecognized function or variable. How do I fix this?

The bottom image shows what my diagram will look like and I can't seem to find big black box anywhere which connest my 4 outputs, x1,x2,x3,x4.

Any help please?

Answer 1

[Fangjun Jiang]

It is a "Mux" block or a "Bus Creator" block.

[Avnish Patel]

Thanks for your response.

And do you know how to fix those undefined function or variables?

[Fangjun Jiang]

You just need to assign the variable in the base workspace, e.g. mgk=1;

[Avnish Patel]

Last question, How do I add equations on the wires? I can set the variables but not entier equations.

Thanks again