[Maxima-bugs] [maxima:bugs] #4640 Erroneos result of funcsolve

[Daniel V. <dan...@us...>]

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**[bugs:#4640] Erroneos result of funcsolve**

**Status:** open
**Group:** None
**Created:** Mon Dec 01, 2025 07:40 AM UTC by Daniel Volinski
**Last Updated:** Mon Dec 01, 2025 07:40 AM UTC
**Owner:** nobody


With the following lines:

eq:(n+1)*f(n)-(n-1)*f(n-1)=(n+1)/(n-1);
funcsolve(eq,f(n));

I get the following result:

(n+1)*f(n)-f(n-1)*(n-1) = (n+1)/(n-1)
f(n) = (%0*n^2+%1*n+%2)/((n-1)*(n+1))

Which contain %0, %1, %2. This solution is bogus.

Barton Willis suggested using trace(solve);
before the command funcsolve to get:

Barton Willis wrote:

Here solve returns the empty list, but it goes ahead and returns a bogus solution:

%i3) funcsolve((n+1)*f(n)-(n-1)*f(n-1)=(n+1)/(n-1),f(n));
1" Enter "solve" "[[%1-%0-1,2*%2-2*%1+4*%0-1,-%2+3*%1-5*%0,4*%0-%1,-%0],[%2,%1,%0]]

1" Exit  "solve" "[]

(%o3) f(n)=(%0*n^2+%1*n+%2)/((n-1)*(n+1))

Daniel Volinski


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