[rrd-users] Re: rrdtool graph question
Alex van den Bogaerdt
alex at slot.hollandcasino.nl
Tue Jun 19 15:31:31 MEST 2001
Raymond Vermeer wrote:
> does anyone no how to do the following ?
> I have a rrdfile with 3 GAUGE datasources A, B and C.
> Now I want to graph the following formula on a line or area :
>
> (A + B - C) / (A + B)
I'll give it a try but first I want to ask you something:
Did you read the tutorial on RPN ?
If yes: what was difficult to understand ?
Anyway, divide the problem in smaller portions:
x1 = (A+B-C)
x2 = (A+B)
result = x1 / x2
divide x1 further:
xx1 = A + B
result = xx1 - C
Paste everything into RPN:
A,B,+,C,-,A,B,+,/
Sanity check, by following the same rules as RRDtool does:
Complete line: CDEF:result=A,B,+,C,-,A,B,+,/
stack after first calculation (A+B),C,-,A,B,+,/
stack after second calculation (A+B-C),A,B,+,/
stack after third calculation (A+B-C),(A+B),/
stack after fourth calculation (A+B-C)/(A+B)
I didn't exactly test it but I don't think I made a mistake. Anyway,
use at own risk (as always by the way).
HTH
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