Hi David,
In general whenever we want to do real time communication between two programs/processes, we use UDP or TCP/IP to communicate.
However, I am not sure exactly what you mean by "MATLAB nested in PureData", you can write to a port using the "udpport" function. On the receiving end for PureData, you can use the "netreceive" function.
The documentation for both are:
netreceive : https://pd.iem.sh/objects/netreceive/
Feel free to follow up with a little more information, like the code and sample data you are using to perform the task.
Hope this helps.