PTP-SD is a type of algorithm.
PTP stands for "probabilistic tree pruning" SD stands for "sphere decoding"
PTP-SD is a type of algorithm that uses PTP with SD.
My question is about the use of the hyphen here. In the paper I am currently editing, the author has written the following:
"Increasing radii algorithm (IRA)  and probabilistic tree pruning with sphere decoding (PTP-SD)  reduces the complexity by adopting the different radii in each layer instead of fixed radii used in the literature."
In such examples, the spelled out form contains no hyphen. Is this okay? Should there be one? If so, where should it go? Why should only the abbreviation contain a hyphen but not the spelled out form?