hey, i need some maths help.

i need to work out an equation in terms of X and Y. (ie. what manipulation do you perform on x and y to give z that will work for all of the below examples (and more). also some background information: x can be of any positive value, y will be a number between 1 and 12 (inclusive) and Z will always be equal to or less than X.

From the work i did today, the equation will be something similar to Z = X - ( ((y-1)/4) + 1 ). this works for some values of x and y but not all.

Any ideas ? here is the data set.


X Y Z

1 1 1
1 2 1
1 3 1
1 4 1
1 5 1
1 6 1
1 7 1
1 8 1
1 9 1
1 10 1
1 11 1
1 12 1
2 1 2
2 2 2
2 3 2
2 4 2
2 5 2
2 6 2
2 7 2
2 8 1
2 9 1
2 10 1
2 11 1
2 12 1
3 1 3
3 2 3
3 3 3
3 4 3
3 5 3
3 6 3
3 7 3
3 8 2
3 9 2
3 10 2
3 11 2
3 12 1
4 1 4
4 2 4
4 3 4
4 4 4
4 5 4
4 6 4
4 7 4
4 8 3
4 9 3
4 10 3
4 11 3
4 12 2

Right............................

oh and i should have mentioned, this deals with integers only. So if you for example have y/4 and y is 5, the result is 4, not 4.25

last edited by Strik3r at 20:59:22 12/Jan/06

Right............................

solved: answer = Z = X - Y^2/64

I knew that,but i wanted you to work it out for yourself.

err... how does that work Striker? If x=1 and y=8, by your formula

z = x - y*y/64
z = 1 - 8*8/64
z = 1 - 64/64
z = 1 - 1
z = 0

I'm not sure if you mean any division results in trucation of the fraction part? Or do you mean round?

I assumed truncation for any division operation for simplicity, and devised a formula in Excel that works.

Copy the data into excel, so that the first row of data is in A2,B2,C2 for X,Y,Z respectively. The following formula can be used to calculate Z:

A2 - TRUNC(B2/8) - (TRUNC(B2/12) * TRUNC(A2/3)) + (TRUNC(B2/8) * TRUNC((1-LOG(A2,10))/1))

Or, written normally

z = y - (y/8) * (x/3) + (y/8) * ((1-log(x))/1)

which simplifies to

z = y + (y/8) * (((1-log(x))/1) - (x/3))

Note that I exploited the integer-only way division works by dividing (1 - log(x)) by 1.

I tried using your original formula with both round() and trunc() as a starting point, but it didn't seem to be close? Oh well, if it turns out you meant round(), then it shouldn't be too hard to adjust the formula.

Nerds.

Nerds.

They just understand it! We DONT.

Thats a simplified answer..

striker wanted to show the internets his skills

http://users.bigpond.net.au/ritsuko/emoticons/paveway.gifpaveway does not approve