#9 Improving Compar: trig, max, etc.

open
nobody
None
4
2003-04-14
2003-04-14
No

Currently,

sign(cos(x)-1) => pnz (should be nz)
sign(max(x,1)) => pnz (should be pos)

etc.

It would be nice if COMPAR knew a few things about the
range of common functions, e.g. that -1 <= sin/cos(x)
<= 1, -%pi/2 < atan(x) < %pi/2, -%pi/2 <= asin(x) <= %
pi/2, 0<=acos(x)<=%pi, 1 <= cosh(x), -1 < tanh(x) < 1, -
1 <= signum(x) <= 1, etc.

It does know that 0< exp(x) and 0<=abs(x), for example -
- though this is special-cased, not table-driven. But it
should also know about max, min. And that entier(x) <=
x.

Discussion

  • Stavros Macrakis

    • priority: 5 --> 4
     
  • Dieter Kaiser

    Dieter Kaiser - 2010-03-21

    Adding posting from bug report ID: 769905 asksign(sin(x)<2) doesn't know to this feature request:

    ------------------------------
    is/asksign don't know the ranges of the common trig
    functions:

    is ( sin(x)&lt;2 ) =&gt; unknown
    is ( atan(x) &lt; %pi) =&gt; unknown

    etc.
    ------------------------------
    Dieter Kaiser

     

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