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I have been working on and off (at home) on that single algorithm for almost 2 and half years, I think.
I am now very close to completion with an elegantly simple algorithm 
Except.. it doesn't work...
After days of staring at my screen I came up with a test that shows an internal data inconsistency that will predict failure.
But... basically the validation is a loop doing some calculation at each step.. .
It came literally right after the same loop applying the calculation result.. yet it has different value than expected?!
Why, ho why? And how? 
I think the forces that be are preventing me from finding the truth! 
That's the only logical explanation I can come up with!
Need exorcism ASAP!    
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Use the debugger? The VS one can break when a variable is modified, so if a value is changing and you don't expect that it may give you an idea where it is being changed from?
Or fill your PC with Pea Soup[^] and have a ball!
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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There is still the Pea Soup option! 
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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That's the only solution! I fear!
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333 is half of the mark of the beast. there's your problem right there. Your code is summoning demons.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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OMG! it is so obvious now that you say it!
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Super Lloyd wrote: it describe 2 potatoes intersection
That explains it.
Your computer's got the wrong chips.
I wanna be a eunuchs developer! Pass me a bread knife!
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Ha! Forget 586!
Sour cream and chilly is the way of the future! 
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haha, help us potato man! you are our only hope!
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just wave a dead chicken over it. it works for me.
of course YMMV my computer is just an old head in a jar that i put a hex on - linux will run on anything these days.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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Lots of good tips in here! 
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in all seriousness, I just got done with tackling a similar debugging issue.
Sometimes the debugger just isn't enough. As another commenter pointed out, the algorithm doesn't usually make much sense to people once it's at the point where it breaks.
So you should write more code. I dumped intermediary LALR tables to CSV for example so i could visualize them. I also made symbols and grammar rules print out string representations of themselves to the debugger to help.
In the end, write MOAR CODE until the problem reveals itself.
Sometimes using graphviz can help, in extreme cases.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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Yeah I made (some tiny bit) of progress lately.. because I wrote plenty of tools and visualisation to make the issue more understandable...
I am getting close.. When it fails I got 3 intersection between 2 shapes (best understanding, so far, about the problem) now I just have to find out why!
That can't be.. I guess I misdiagnosed a touch for an intersection.... That's a tricky one, since intersection are approximation though...
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I'm building a parser generator right now, so if you know what that entails, you know I mean it when I say I feel your pain, neighbor.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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I have used a few of them, they are good!
They are also tricky beast!
Good luck with that! And thanks for the support!
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In my past I did a lot of geometric programming. Something we had to be be very careful of was degenerate intersections and numerical tolerance. That is the first thing I thought of when you mentioned an odd number of intersections. If you are at or very close to the endpoint of a line segment, it might miss, or hit, when it really shouldn't.
Sometimes you have to catch them and handle them specially (*cough* hack *cough*). Like artificially extend the vector slightly to see if it intersects within the segment, or keep intersections that are questionable conditional until you can tell the count is right. For instance, imagine two line segments whose common endpoint is on or very close to the segment you are intersecting with. Really, there should be only one intersection there. But if you count each segment endpoint as colliding, then you get two intersections where you should have only one. Or vice versa, you might discard both because you think they are off the line, and have zero where you should have one.
Sorry, this is off the top of my head remembering stuff we had to deal with a long time ago.
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Hey I am pretty sure it is such error.. it only happen (so far as I know) with 2 almost parallel shape and one with 1 very small edge...
Anyhow can't do anything more about this week, preparing a table top RPG adventure..
But gods this is so frustrating...
For the record to get around such issue I merge many point that I found close to each other, nudging them slightly.. But that is not enough... Now I also use smarter crossing edge detection at intersection, still not enough..
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That's how I have solved some knotty issues with a Python bouncy ball simulation I have been writing(just because I wondered what all the hype about Python has been).
I created a logger class and wrote all the data out to a tab delimited file.
I then found fairly quickly where the issues were - as rather than see isolated data, which is what debugger information tends to present, I was able to see data over time and solve the problem from there.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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Frankly, I solved that by not coding in python =P
It's a magical language in some ways, but the grammar was designed at gunpoint.
Who uses tabs to dictate program flow?
I protest the language out of my distaste for poor grammars
/grammar nazi
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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Quote: Who uses tabs to dictate program flow?
A thing I'm asking me all the time.
It does not solve my Problem, but it answers my question
modified 19-Jan-21 21:04pm.
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i mean, it's one thing to use tabs to show program flow, but they should be descriptive, not prescriptive.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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Yes yes, I'm with you on this, and I think all who ever wrote a parser/compiler will agree. WhiteChars _are not_ an instrument to be a part of the gramatics.
It does not solve my Problem, but it answers my question
modified 19-Jan-21 21:04pm.
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Once you get used to it, the spacing makes a lot of sense.
I find it easier to follow programme flow with the indentation.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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