Challenge: figure out why this loop doesn't stop

[Sparkette]

I have a challenge for you: looking at this VI snippet, it appears that this loop should stop after 11 iterations. However, when you click Run Once, it doesn't stop. See if you can figure out why it doesn't stop.

 

 

Hint (if it really is much of a hint): it uses a trick I sincerely doubt you've ever seen before!

 

If you don't have LabVIEW 2015 (or don't feel like loading it from a VI snippet), here's a version that should work on versions as far back as 2009:

 

LV2009.viFetching info...

[JKSH]

:-S What did you DO to the subtract node?!

[ShaunR]

+ and - primitives use the compound arithmetic node, IIRC. I expect you set the first terminal to invert?

 

What do we win if we get it right?

Edited August 22, 2015 by ShaunR

[Sparkette]

  On 8/22/2015 at 6:32 AM, ShaunR said:

+ and - primitives use the compound arithmetic node, IIRC. I expect you set the first terminal to invert?

 

What do we win if we get it right?

 

It's clearly not a compound arithmetic node. Is there a way to make one look like a regular subtract node or something?

 

And you don't win anything; I'm just curious if anyone will figure it out.

Edited August 22, 2015 by flarn2006

[drjdpowell]

Did you wire up the minus as 2-(shift reg), then move the wires around to make it look like (shift reg)-2?

 

Then the shift reg would go 10, -8, 10, -8,… and never be less than -10.

[pawhan11]

Replaced subtract node and now works as it should Why I have no idea ...

[LogMAN]

  On 8/22/2015 at 8:00 AM, drjdpowell said:

Did you wire up the minus as 2-(shift reg), then move the wires around to make it look like (shift reg)-2?

 

Then the shift reg would go 10, -8, 10, -8,… and never be less than -10.

 

I guess you are right, however the wires are not wired around, the Subtract function is actually flipped horizontally :

 

 

I'm still trying to figgure out how you did that, flarn2006...

Please tell me if it is not possible from within LabVIEW or I die before solving this

[JKSH]

I'm guessing h

 

  On 8/22/2015 at 12:03 PM, LogMAN said:

I guess you are right, however the wires are not wired around, the Subtract function is actually flipped horizontally :

 

Flipping Magic.png

 

I'm still trying to figgure out how you did that, flarn2006...

Please tell me if it is not possible from within LabVIEW or I die before solving this

 

I'm guessing he used his backdoor VI editor (https://lavag.org/topic/19178-low-level-vi-data-editor-warning-not-for-production-use/) to create a mutant subtract node 

[JackDunaway]

dcoFiller=0x2 apparently swaps mapping of parameters to instruction, and also prevents the top wire from becoming a stomper. 0/10, would not recommend; stick to dcoFiller=0x3

[LogMAN]

  On 8/22/2015 at 12:35 PM, JKSH said:

I'm guessing he used his backdoor VI editor (https://lavag.org/topic/19178-low-level-vi-data-editor-warning-not-for-production-use/) to create a mutant subtract node 

 

That is cheating!

... But I guess you are right.

 

  On 8/22/2015 at 12:49 PM, JackDunaway said:

dcoFiller=0x2 apparently swaps mapping of parameters to instruction, and also prevents the top wire from becoming a stomper. 0/10, would not recommend; stick to dcoFiller=0x3

 

Hehehe... Found a new toy to trouble our trainees with.

Edited August 22, 2015 by LogMAN

[Sparkette]

  On 8/22/2015 at 12:35 PM, JKSH said:

I'm guessing h

 

 

I'm guessing he used his backdoor VI editor (https://lavag.org/topic/19178-low-level-vi-data-editor-warning-not-for-production-use/) to create a mutant subtract nod

 

Correct!

More specifically, I switched the "bounds" properties of the two input terminals.

[JKSH]

  On 8/22/2015 at 6:47 PM, flarn2006 said:

Correct!

More specifically, I switched the "bounds" properties of the two input terminals.

 

Please ensure that your genetically-modified nodes don't escape into the wild! 

[Sparkette]

  On 8/22/2015 at 11:52 PM, JKSH said:

Please ensure that your genetically-modified nodes don't escape into the wild! 

 

Don't worry; the default palette is 100% organic.

Edited August 23, 2015 by flarn2006

[X___]

Replacing the Subtract operator by the Compound Arithmetic one fixes the sickness.