Solve and NSolve hitting iteration limit for simple system

Question

I'm am trying to get Mathematica to determine the intersection of a line and a parabola, like so:

Solve[{x + y == 6, x^2 == y}, {x, y}]

But evaluating this gives Recursion depth of 1024 exceeded. and Iteration limit of 4096 exceeded.

Does this problem need to be expressed in some other way?

Try it again in a fresh Mathematica session – Dr. belisarius May 08 '15 at 23:45 — Dr. belisarius, May 08 '15 at 23:45
You surely have defined xor y previously – Dr. belisarius May 08 '15 at 23:46 — Dr. belisarius, May 08 '15 at 23:46
Thanks @belisarius, that was indeed the problem. :/ – billc May 08 '15 at 23:51 — billc, May 08 '15 at 23:51

score 2 · Accepted Answer · edited Apr 13 '17 at 12:56

2

As @belisarius noted, the problem here is that x and y were defined at an earlier point in the Mathematica session.

This kind of error can be prevented like so:

Block[{x, y}, Solve[{x + y == 6, x^2 == y}, {x, y}]]

which localizes x and y, correctly giving:

{{x -> -3, y -> 9}, {x -> 2, y -> 4}}

This problem is discussed in more detail in the Lingering Definitions section of Pitfalls for New Users.

edited Apr 13 '17 at 12:56

Community

answered May 08 '15 at 23:56

billc

Speaking as a new user I also recommend to make use of ? or ?? rather often to see if variables and or functions are internally implemented as desired. If not, as you mentioned Blockwould be a workaround or to use Clear – Spaced May 08 '15 at 23:58
1

If we are going to take walkarounds ..Solve[{\[FormalX] + \[FormalY] == 6, \[FormalX]^2 == \[FormalY]}, {\[FormalX], \[FormalY]}] – Dr. belisarius May 09 '15 at 00:01

1 Answers1