Is there some kind of limit on the complexity of equations for W|A "solve"

[dylanwilliams]

I was trying to use Wolfram Alpha to solve some complicated equations and I was getting error “Wolfram|Alpha doesn’t understand your query”

so i started playing around with a few test cases and it seems to be an equation complexity/length constraint.

if I enter
solve b = a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a for a
I get the expected result (a = b/23), but if i enter it with just one more a as follows
solve b = a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a for a
instead of getting (a = b/24) i get “Wolfram|Alpha doesn’t understand your query” error.

any ideas? I have some really long equations that id really like to rearrange by variable, and it would take ages to do by hand

thanks,
-Dylan

[sghuisman (Sander Huisman)]

multiple things could be the reason, I can only speculate:

Depending on the length of the input there might be different heuristics of what to do with it. e.g. if it is short, it is more probably to be (say) an animal name, then when it is a very long input. Perhaps a similar construct is in place for equations.

Also, there might be a construct in place that makes sure that (very long) input does not crash or unnecessarily overloads the system.

Perhaps you can run it in the Wolfram Cloud or (if available) on your own computer using Mathematica.

[mthiel (Marco Thiel)]

Hi,

Interestingly, a Wolfram|Alpha request from within Mathematica works just fine:

Cheers,

M.

[dylanwilliams]

what about 25 or 30? i should have mentioned earlier, i did get inconstant results, sometimes it would accept 24, but not 25, sometimes it would accept 23 but not 24 etc

[mthiel (Marco Thiel)]

Hi,

can confirm that. As you say sometimes 24 works sometimes it does not. I would not have expected this to give different outputs. It does not appear to be related to some server time to parse the input either.

Cheers,

M.

[mthiel (Marco Thiel)]

Here is something a little bit more systematic. The following code generates Wolfram|Alpha queries with different numbers of “a’s”.

results = 
  Monitor[Table[{i + 1, First@(List @@ WolframAlpha[Evaluate@StringJoin[Join[{"solve b=a"}, Table["+a", {i}], {" for a"}]], {{"Result", 1}, 
 "FormulaData"}])}, {i, 1, 40}], i];

It turns out that the interesting one is at the transition at 24 a’s. The following runs 40 trials of that one request.

results2 = 
  Monitor[Table[{i,First@(List @@ WolframAlpha[Evaluate@StringJoin[Join[{"solve b=a"}, Table["+a", {23}], {" for a"}]], {{"Result", 1}, 
  "FormulaData"}])}, {i, 1, 40}], i];

Here are the results in two tables:

TableForm[{{Grid[Join[{{"Number a's", "Result"}}, results], Frame -> All], Grid[Join[{{"Trial", "Result"}}, results2], Frame -> All]}}]

Cheers,

Marco