solve failure

[Albert Chan]

(12-01-2021 09:44 AM)Nigel (UK) Wrote:  I cannot reproduce your problems on my machine, but storing a function in \(x\) does cause the solve() to fail.

I tried on HP prime emulator, build 2.1.14181 (2018 10 16)
There is a bug for solve, with pi in it.

Cas> purge(x)
Cas> k := 10^6
Cas> solve(3.0*k = k*10^5*π^2/x^2,x)       → {−573.573720955,573.573720955}
Cas> k *= 10
Cas> solve(3.0*k = k*10^5*π^2/x^2,x)       → {−573.573720955,573.573720955}
Cas> k *= 10
Cas> solve(3.0*k = k*10^5*π^2/x^2,x)       → []

Same behavior if we replace 3.0 with integer 3

BTW, XCas had the same bug.
But, if we use integer 3 instead, the bug show up much later.

XCas> k := 10^93 :;
XCas> solve(3*k = k*10^5*π^2/x^2,x)       → [-100*√(30)*pi/3, 100*√(30)*pi/3]
XCas> k *= 10 :;
XCas> solve(3*k = k*10^5*π^2/x^2,x)       → []

Pulling pi^2 outside solve fixed it.

XCas> solve(3*k = k*10^5*c/x^2,x) (c=pi^2) → [-100*√(30)*pi/3, 100*√(30)*pi/3]

Pi bug should be fixed. For now, use fsolve instead.