Re: [Reduce-algebra-developers] how to zero small coefficients in combined numeric-algebra

[Prof T. R. <Pro...@pr...>]

Hi,

thanks for this procedure, works so far.  Two questions follow:

On 24/2/2024 8:01 pm, Arthur Norman wrote:
> symbolic procedure kill v;
>     if floatp v and v <= 1.0e-6 then 0.0
>     else if atom v then v
>     else kill car v . kill cdr v;

1.  Why do I not need  "abs(v)<="  I can see in the trace that so 
far negative values appears to be always stored as (minus 
positive-number) so abs(v) is apparently not needed, but is that 
really always the case?

2.  In the interim I have found that my current problem really needs 
the threshold to vary depending upon the overall norm of stuff that 
I am dealing with, so I want to code something like

symbolic procedure kill v;
    if floatp v and v <= tolerance then 0.0
    else if atom v then v
    else kill car v . kill cdr v;
...
on rounded;
for i:=1:99 do begin
...
tolerance:=1e-8*normStuff;
kill(v);
...
end;

But then kill(v) fails.  I have tried declaring "share tolerance;" 
but that also fails.

Tony

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* (2020) Linear Algebra for the 21st Century
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https://global.oup.com/academic/product/linear-algebra-for-the-21st-century-9780198856399

* (2015) Model emergent dynamics in complex systems
SIAM, Philadelphia. isbn: 9781611973556.
https://epubs.siam.org/doi/10.1137/1.9781611973563

* (2009) Elementary calculus of financial mathematics
SIAM, Philadelphia. isbn: 978-0-898716-67-2.
https://epubs.siam.org/doi/10.1137/1.9780898718225

* (1994) A one-dimensional introduction to continuum mechanics
World Sci. isbn: 978-981-02-1913-0.

* (2020) with John Maclean, and J. E. Bunder; Equation-Free
function toolbox for Matlab/Octave.
http://github.com/uoa1184615/EquationFreeGit

Emeritus Professor A.J. Roberts,  FAustMS
School of Mathematical Sciences,  University of Adelaide
https://profajroberts.github.io/
mailto:Pro...@pr...
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