Short question about probability amplitudes

[nomadreid]

When one says the probability amplitude for a quantity when it has probability P, which one does one take, the a+bi or the a-bi?

 

[facenian]

I don't understand your question, perhaps you should try with an example

 

[mathman]

When one says the probability amplitude for a quantity when it has probability P, which one does one take, the a+bi or the a-bi?

I am not fully familiar with the subject, but it is either |a+ib| or a² + b²

 

[Ken G]

When one says the probability amplitude for a quantity when it has probability P, which one does one take, the a+bi or the a-bi?

I think the problem is, you are asking the question backward. Many probability amplitudes give the same probability, so you can infer the probability from the amplitude, but not the other way around. Thus your question is like asking how old are all the people who have a May 1 birthday.

 

[nomadreid]

Thanks for the replies.
First, Ken G knew what I was talking about, and his answer makes sense: I gwould guss from his reply that all contexts are "given the probability amplitude A find the probability amplitude B"... ; and none in which you need to find the probability amplitude B given the probability of A. I'll accept that.
Mathman misunderstood my question: I was not asking for the amplitude (which is a² + b²) but the probability amplitude (which is a+bi such that a² + b² = the probability.)
Finally, facenian would like an example of what I am referring to. I am referring to the ψ which you find in quantum mechanics; for example in Schrödinger's equations.

 

[Ken G]

I think you have it now!