Maths Challenge!!!

[newtron]

This program that I am working with generates a 1-D radial grid by defining radial increments that increase from one to the next by the same factor :

ΔR(n+1) = f * R(n)

The user provides NLOG (number of interface radii desired), RLOG (desired radius of the last (largest) of these radii), and DR (the reference radial increment : the first ΔR generated will be equal to f * DR). So my question is: How is f calculated?

[newtron]

Oops, the I forgot a delta. The equation should be:

ΔR(n+1) = f * ΔR(n)

I believe this can be written as the following series:

RLOG = DR * (f + f ^2 + f ^3 + ...+f ^NLOG)

I don't know where to go from there. It's been a long time since I've worked with series. Is there an easier way?

I guess it doesn't matter. The program does it. I was just curious.

[mibn2cweus]

f = Δr(n+1)/Δr(n)

[newtron]

mibn2cweus, the equation that you just rearranged is only useful if f is a known constant. f needs to be calculated as a function of the variables provided by the user.

[potterfan3]

no idea

[dyli795]

Coinsidentaly, me niether.

[newtron]

Come on. Surely there is a way to solve the above finite series for f, which is the only unknown.