EPICS V4 Telecon, 15-Apr-2014.
1. N-types for units and error (greg).
2. Demo using pva and easyPva from within matlab (greg). [Not covered. See meeting 29-Apr-14]
Present: BD, GC, MK, MS, GW, NM
NEW TOPIC: Proposal for normative types
GW: not try to match error and value type
MS: error could just be a double
GC: Why not have statistics type
GW: we do: NTAggregate
When creating a table, should we have a column of an NTAggregate, or multiple name column with average, stddev, …
GC: multiple column (I’d rather converge to a general purpose case)
GW: single column of aggregate type (I want to keep the semantic association)
GW: we’ll need to try
NM: we could use the archiver
GW: will try to use the proposal for data from an archiver
1. Units are already in N-Types, as I said before, they're in
display_t so they're already in all types.
a) Add error and N (number of observations) to NTScalar and
b) The rule that a type must not be composed of any other types
is removed. That way, we can define the higher types like
NTTable in terms of NTScalar and NTScalarArray.
scalar_t error :opt
scalar_t n :opt
scalar_t  value
scalar_t  error :opt
scalar_t  n :opt
Error communicates the error bars of each element of value. That
is, error SHOULD NOT be used to communicate the computed error
of the set of values in the value field. Thereby, the length of
error MUST be equal to the length of value. Call length of value "M".
n MUST be length = 1 or M.
If length 1, then the value of n should be taken to range for
all elements of error. For instance, in a synchronous
acquisition system, where 300 diagnostic devices are all sampled
on a 100Hz signal, and we wish to encode the average reading and
RMS of each device over (the same) 5 cycles in one
NTScalarArray. Then length of value = 300, length of error =
300, and length of n = 1 (and has value = 5). Incidentally, the
100Hz nature of the acquisition would have to be encoded
elsewhere, possibly in the display_t.description field.
So, using NTScalarArray for NTTable:
string  labels
Conclusion: Maybe N-types should make a formal association between all value fields and their error, whereas V-types don’t, they’re oriented toward being general purpose.
So remains to be seen whether that makes sense or is just bullshit.
Matlab demo in 2 weeks.