Multi - key homomorphic encryption

[umermjd11]

In ML we have the model weights in signed float forms. In federated settings, how can we homomorphically support these two operations under single-key holomorphic encryption settings as well as multi-key homomorphic encryption settings?

1. Multiplication with scalar w, where w belongs [0,1]
2. Addition of cypertexts

I believe there are different homomorphic encryption schemes for these operations with

1. unsigned integers
2. signed integers
3. unsigned floats
4. signed floats

Please explain and indicate them, also provide the code?