[MUG] Too many levels of recursion

[MUG] Re: Too many levels of recursion
Author: Maple User Group    Posted: Tue, 19 Nov 2002 16:52:50 -0500
>> From: Maple User Group "maple_gr" | >> From: "guyer" | Has anybody an idea about the error message "(In Signature) Too many | levels of recursion" ? Is it my procedure's fault or not? | Is this problem concerned with the hardware of the computer which I | can solve by adding more memory? -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=- Date: Fri, 15 Nov 2002 12:49:14 -0500 To: "maple-list" From: "Gerald A. Edgar" "edgar" Subject: Too many levels of recursion In my experience, it is a sign of INFINITE recursion, where something (perhaps indirectly) depends on itself. So whenever I have received this message, it has been my fault. Try turning on "trace" for the function where this happens, and see if you can tell what is going on. -- G. A. Edgar http://www.math.ohio-state.edu/~edgar/ -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=- Date: Fri, 15 Nov 2002 13:55:24 -0500 (EST) From: Carl Devore "devore" To: MAPLE User Group "maple-list" Subject: Too many levels of recursion Most likely you have a statement of the form x:= x+1 somewhere where x has not been initialized. > Is this problem concerned with the hardware of the computer which I > can solve by adding more memory? No. -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=- Date: Fri, 15 Nov 2002 13:44:42 -0800 (PST) From: Robert Israel "israel" To: MAPLE User Group "maple-list" Subject: Too many levels of recursion |> Has anybody an idea about the error message "(In Signature) Too many |> levels of recursion" ? Is it my procedure's fault or not? Yes, probably. It might help if we could see the actual procedure, but usually this message indicates that somehow you are setting up an infinite recursion. The other possibility is that this is a procedure that legitimately uses a very large number of levels of recursion. Each time a procedure calls another, some information must be stored in an area of memory called the stack. This is removed when the called procedure returns. The stack has only a finite capacity, and when it is full this error message occurs. The size of the stack may vary depending on the platform and the version of Maple as well as the amount of available memory in the computer. For example, the following recursive procedure, if called with a positive integer n, will at some point have n "levels of recursion" active at the same time, as f(n) calls f(n-1) which calls f(n-2) and so on down to f(1). > f:= proc(n) if n = 1 then 2 else f(n-1)^2 + 1 mod (n+2) fi end; When I tried it just now (in Maple 8 under Windows NT 4.0), f(3309) worked but f(3310) gave me "too many levels of recursion". It is often possible to rewrite a recursive procedure as an iterative one, and there are various other tricks that can reduce the amount of recursion needed. > Is this problem concerned with the hardware of the computer which I > can solve by adding more memory? Probably not. Robert Israel "israel" Department of Mathematics http://www.math.ubc.ca/~israel University of British Columbia Vancouver, BC, Canada V6T 1Z2 -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=- Date: Sat, 16 Nov 2002 10:18:46 +0100 From: Maerivoet Roland "roland.maerivoet" To: "maple-list" Subject: Too many levels of recursion Hello, I guess it has to do with your procedure. Since you did not include it, it's rather difficult to give exact comments. You get this kind of error-message when using variables recusively. -- Met vriendelijke groeten - Best Regards Roland Maerivoet Hogeschool Gent Departement Bedrijfskunde Aalst Keizersplein, 19 B9300 Aalst Belgium tel: +32053212321 fax: +32053710934 http://docent.hogent.be/~roma754 http://users.pandora.be/roland.maerivoet -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=- From: "Dr Francis J. Wright" "F.J.Wright" To: "guyer" Subject: Too many levels of recursion Date: Mon, 18 Nov 2002 11:21:42 -0000 > Has anybody an idea about the error message "(In Signature) Too many > levels of recursion" ? Is it my procedure's fault or not? Probably. > Is this problem concerned with the hardware of the computer which I > can solve by adding more memory? Probably not. This error usually arises from a recursive procedure that has an error in the base case (i.e. the test that should stop the recursion). I suggest that you try running your procedure in the debugger, or just increase printlevel and let the procedure run for a bit. From the output, you may be able to spot the problem. But beware that you will probably get a LOT of output! IIRC, there was a time when the Windows version of Maple had a rather small stack allocated and some highly recursive library procedures could run out of stack and so cause the above error, but I don't think that has been an issue for some time now. It probably related to early releases of Maple V for Windows 3.1. If you did not intend to write a recursive procedure then maybe you have done so unintentionally. A recursive procedure is one that calls itself, which is fine (and a very powerful programming technique) provided you remember to include an appropriate base case (or cases) to stop the recursion. Francis

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