why is my hp prime giving me the wrong answer

[C.Ret]

(11-10-2024 06:07 PM)Albert Chan Wrote:  

(11-10-2024 02:47 PM)C.Ret Wrote:  What is the use of this epsilon parameter I found in the second page of the CAS settings menu?

It is a global variable, and can be use for anything, by anyone.
What comes to mind is solver, linsolve, rref, exact (althought it does not honor setting if ε=0) ...

You should have added RREF to your list, because thanks to your explanation, I just discovered that guest2112 could have had the right answer directly in the HOME mode by simply adjusting the value of epsilon in the second page of the CAS setup menu!

Indeed, the screenshots below show how with the default value of 1.E-12, the RREF instruction fails to reduce M1.

But, by replacing this value with a more realistic one (such as 1.E-05 in my capture), we may obtain immediately the correct result:


Note that I use the "Floating 3" numeric format in order to have a more readable capture where the numbers are displayed with a limited number of decimals. Of course, the M1 matrix does contain internally the values ​​in full precision.

In CAS mode, curiously, a system message tells me that a lower value 1e-6 replaces my setting. Obviously, CAS mode allows you to get rid of the problem of precision or rounding errors by entering the matrix M1 in an exact form.
Nevertheless, the proposed precision of 1e-6 allows to obtain a correct numerical reduction of M1. Infact, correct numeric result appears at \( 1.1197\textbf{E-12} \cong 2^{-39.7} \).

Every day I discover new aspects of this mischievous HP Prime.

Too bad there was no system message to warn guest2112 that RREF was not finding a correct solution and was struggling with an unsuitable epsilon for his matrix!