OpenEuphoria

Re: Algebra problem

• Posted by Derek Parnell <ddparnell at bigpond.com> Jul 08, 2005
• 578 views

Erik-Jan van Kampen wrote:
> 
> Derek Parnell wrote:
> > 
> > My high school algebra has deserted me 
> > 
> >  Given the formula 
> > 
> >    A^b + Cb = d
> > 
> > how do I solve for 'b'?
> > 
> > -- 
> > Derek Parnell
> > Melbourne, Australia
> > 
> 
> Hi Derek,
> 
>  From the Matlab 6.5 Symbolic Toolbox:
> 
> >> solve(A^b+C*b-d,b)
>  
> ans =
>  
> -(lambertw(log(A)/C*exp(d*log(A)/C))*C-d*log(A))/log(A)/C
>  

Thanks. I thought it would be something simple like that ;-0

This solution also implies that 'A' must > 1 and 'C' must be > 0 otherwise there
is no valid value for 'b'.

For those curious about this formula, it is being used in project task
estimations. Given an estimated duration and a confidence rating, I try to
calculate reasonable minimum and maximum durations for the task.

For example, if a task has had 12 days work already expended and the project
manager estimates with 75% confidence that there is another 5 days to go, I'm
calculating what are the optimistic and pessimistic durations for the task. Other
variables include how experienced (skillful) the manager is in estimating things.

The formula above is one of the trickier ones involved. I have been using
spreadsheets to help record and calculate things but once projects get above a
certain size or complexity, I need another tool. MS-Project falls short in a
number of areas too.

-- 
Derek Parnell
Melbourne, Australia