Well, Ill be compiling it on a VC 6 machine. In truth, I dont think the function should be so complex that you require Linux specific OS calls.Originally Posted by CrazyNorman
As for rashikil's lame attempts to prove his intelligence, Id say he has succeeded, although not in the way he probably intended.
defines a line with slope 0.0 and zero inflection points. Since an input of infinity into your equation produces erronious results, it is hence disqualified.
Last edited by abachler; 07-10-2007 at 01:14 PM.
Now you're making up new rules that weren't in your original set of rules. Sigmoid functions are functions mapping the real line into a subset (a,b) of the real line; infinity is not part of the domain. It's a good idea to have all the rules of the contest listed, if you want the function to handle non-real doubles.
But, if you insist...
This implements the function f(x) = 2atan(x*((((((((100!)!)!)!)!)!)!)!))/pi.Code:double sigmoid(double x) { return (x > 0) - (x < 0); }
Edit: Of course, this would have to be modified if the input is an array of numbers now.
There are 10 types of people in this world, those who cringed when reading the beginning of this sentence and those who salivated to how superior they are for understanding something as simple as binary.
Well, im tired of you claiming this as an entry, so heres the deal. Return 0.0 does not compute a sigmoid. return (x > 0) - (x < 0) returns type bool or an integer depending on your compiler, so it violates rule #2 even as originally defined. Even if you recast it as a double, it would fail based on the requirement that the output exhibit 'the classical properties of a sigmoid'. i.e. a non-zero slope at all points.
entry disqualified.
Before you try to provide some other entry, please go read what a sigmoid function actually is. Its a very specific type of function that none of your entries even approximate as you claim.
Last edited by abachler; 07-10-2007 at 03:01 PM.
I still find it confusing frankly. I can't help but feel that you are ignoring what Rakashil Fol is really attempting to say.
Do you intend to ignore these, and the other points about floating point numbers? Fuzzy math will make correct entries wrong. I don't think anyone will want to participate if the contest judge - I hate the term - doesn't know what he's doing.If you're mapping (-infinity, +infinity) monotonically into (-1,1) or [-1,1] using doubles, you're going to have either significant regions of slope zero, or multiple inflection 'points'. That's what you get when approximating functions' behavior, no matter what the function is. Suppose I wrote
Sigmoid functions are functions mapping the real line into a subset (a,b) of the real line; infinity is not part of the domain.
If the goal of the contest were to plot a sigmoid, then the fastest entry would not actually draw a sigmoid at all, but instead calculate where to plot. Nevermind whether doubles are appropriate for this purpose. Do you intend to write code that would draw a sigmoid curve based on the output, or will those kinds be disqualified also? Would that be weasel code?
No, I use sigmoids all the time. Rashakil is trying to use 'return 0;' style weasel code and then claim it computes a sigmoid. It performs no calculation whatsoever, sigmoid or otherwise. The requirement only to exhibit the features of a sigmoid was intentionally left vague to allow for creative entries, not to act as a loophole for rules lawyers. Yes I understand that a floating point number cant quantize infinite granularity. However the data set returned by ALL his entries fail on multiple points, and yet he refuses to accept that they are not valid entries. I changed the rules, not because they were flawed, but just to spell it out in really small words that even a retarded gorilla can understand that entries must actually compute a sigmoid, not just return a fixed value. Hey im sorry I didnt put in the rule about no weasel code up front. I honestly expected people to submit realistic entries, not to try to claim that since some specific subset of a function cannot be computed within the limits of the hardware, that therefor all attempts at computing any function of that type in hardware can be represetned by a single fixed value. so for those of you that want ot exploit the limitations of the hardware to avoid actual computation, here is a specific requirement of the function.
For all sets of 3 points a , b , and c where a < b < c and all 3 points are in either the positive or negative domain ,the following three conditions must be met:
1. f(a) < f(b) < f(c)
2. the slopes of the function of a , b , c (sa , sb , sc) must exhibit the quality of sa > sb > sc for sets of positive numbers
3. the slopes of the function of a , b , c (sa , sb , sc) must exhibit the quality of sa < sb < sc for sets of negative numbers
Last edited by abachler; 07-10-2007 at 03:53 PM.
This condition is impossible to meet.
How are you defining the slope of a function that maps doubles to doubles?2. the slopes of the function of a , b , c (sa , sb , sc) must exhibit the quality of sa > sb > sc for sets of positive numbers
3. the slopes of the function of a , b , c (sa , sb , sc) must exhibit the quality of sa < sb < sc for sets of negative numbers
There are 10 types of people in this world, those who cringed when reading the beginning of this sentence and those who salivated to how superior they are for understanding something as simple as binary.
I was wondering about that too. In typical applications of a sigmoid, it's required that the function be differentiable, and the value of its derivative is also used. You can of course approximate that with the definition of derivative, but it's better to have a true symbolic derivative available.
I know of several functions that meet all three conditions. In particular -
(1 / (1 + e^-X))-0.5 The logistic function, with an offset
as for defining slope, I believe slope is defined as the first order dirivative of a function. In the case of the limitations of the FPU it would then have to be the smallest measureable differencee between two neighboring values. Since doubles are translated into the 80 bit internal format, I would say the slope defined by a line between the points X-, f(x-) and X+ , f(X+) should suffice for purposes of this contest. Where X- is the largest value representable in 80 bits that is less than X and X+ is the smallest value greater than X. Im talking mathmatically greater or less than, not what the FPU will return, since values very close to one another will be reported as equal.
Last edited by abachler; 07-11-2007 at 10:25 AM.
You can specify if you want the function to be called sequentially, or to be passed the array. The array is to make it fair for GPU entries, since they generally process several data points at once.
