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I have a problem where I have TWO NON-rotated rectangles (given as two point tuples {x1 x2 y1 y2}) and I like to calculate their intersect area. I have seen more general answers to this question, e.g. more rectangles or even rotated ones, and I was wondering whether there is a much simpler solution as I only have two non-rotated rectangles.

What I imagine should be achievable is an algorithm that only uses addition, subtraction and multiplication, possibly abs() as well. What certainly should not be used are min/max, equal, greater/smaller and so on, which would make the question obsolete.

Thank you!

EDIT 2: okay, it's become too easy using min/max or abs(). Can somebody show or disprove the case only using add/sub/mul?

EDIT: let's relax it a little bit, only conditional expressions (e.g. if, case) are prohibited!

PS: I have been thinking about it for a half hour, without success, maybe I am now too old for this :)

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You seem to hope to get an answer using only the field operations ($+$, $-$, $\times$, and $/$). But can you get a formula for the distance between two points on the real line using only those tools? Failing to do so should persuade you that your hope is forlorn. –  Lubin Jan 16 '12 at 20:06
    
I thought because the area of a square would be calculated as (a-b)*(c-d), a negative area would mean that the area is rotating in the other direction (if you use vector). But I think the question is ill-posed anyways. Sorry for wasting time.... –  chaiy Jan 17 '12 at 13:20

1 Answer 1

up vote 12 down vote accepted

Uses only max and min (drag the squares to see the calculation. Forget about most of the code, the calculation is those two lines with the min and max):

http://jsfiddle.net/uthyZ/

You can also reduce min to max here (or the opposite), i.e. $min\{a,b\} = -max\{-a,-b\}$.

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Also, if you really don't want to use max, note that max(a,b)=(|a-b|+a+b)/2. –  Lopsy Jan 16 '12 at 15:29
    
thanks for the answers. It looks like it's easy using non-continuous functions. I was asking this question because my stomach told me that this should be in a form, e.g. Area = A*B-C*D+(A-C)*(B-D). Essentially something without the if condition (max is like if(a>b)?a:b though) –  chaiy Jan 16 '12 at 16:57
    
@chaiy Since the function that takes vertices and returns area is not differentiable, it is not possible to construct this function out of differentiable functions. You must use an "if-like" function in order to do it. –  Tanner Swett Aug 13 '12 at 19:27

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