MaplePrimes - answers and comments on Question, Assumptions - calculations

Look hrere

Kamel Boughrara — Fri, 10 Feb 2012 21:07:35 Z

Look here

http://www.mapleprimes.com/questions/130529-Subs-Command-Bug

Cannot overcome it.

icegood — Fri, 10 Feb 2012 23:35:47 Z

Procedure above fails.

Want after next operators:

assume(a>0);

b:=a;

ReassumeVars([[a<6]]);

b again have VALID value of a and condition on a will be :
is assumed to be: RealRange(-infinity,Open(6))

Brainkiller

icegood — Sat, 11 Feb 2012 00:06:11 Z

ReassumeVars:=proc(pallconditions)
local li, lvar, lcondition;
global DummyVar;
#
for lcondition in pallconditions do
    lvar:=eval(op(1, lcondition[1]));
    for li in anames('user') do
      if not type(eval(li), procedure) and has(eval(li), eval(lvar)) then
        assign(li, subs(eval(lvar)=DummyVar, eval(li)));
      end if;
    end do;
    assume(lcondition[]);
    lvar:=eval(op(1, lcondition[1])); # lvar before not valid anymore!
    for li in anames('user') do
      if not type(eval(li), procedure) and has(eval(li), DummyVar) then
        assign(li, subs(DummyVar=lvar, eval(li)));
      end if;
    end do;
end do;
end proc:

- is it OK? Can you suggest smth else?

something else

Alejandro Jakubi — Sun, 12 Feb 2012 08:37:46 Z

This is a known issue of the assume facility. As you have probably read already in this thread, this facility is actually a patch. So, it might be wiser to make things in another way, e.g by means of assuming (in turn, a kind of patch on assume). In general, it will make the assumptions during the evaluation of the expression and then undoes them, so that it should not further interfere with substitutions and the like:

H:=sqrt(a^2) assuming a>0;
                                     H := a
subs(a=b, H) assuming(a>0);
                                       b

I've read it already

icegood — Fri, 10 Feb 2012 21:45:00 Z

My case relates to every expressions, not only rtables. And expressions assumed to fully calculable (because they are under global scope). Actually i've written workaround:

ReassumeVars:=proc(allconditions)
local li, var, condition;
global DummyVar;
#
for condition in allconditions do
    var:=op(1, condition[1]);
    for li in anames('user') do
      if type([eval(li)], list(symbol)) and evalb(li<>var) then
        assign(li, subs(var=DummyVar, li));
      end if;
    end do;
    assign(evaln(var), evaln(var));
    assume(condition[]);
    for li in anames('user') do
      if type([eval(li)], list(symbol)) and has(li, DummyVar) then
        assign(li, subs(DummyVar=var, li));
      end if;
    end do;
end do;
end proc:

with input [[a<=amax, a>=amin], [b is real]] or whatever. Should work.

assuming is not universal

icegood — Mon, 13 Feb 2012 17:09:10 Z

'assuming' is not universal, at least doesn't work in my case. While for subject i found way to get new realigned pointer after 'assume' calling.

if evalb(convert(lvar,string)[-1..-1]="~") then
      lvar:=FromInert(_Inert_ASSIGNEDNAME(convert(lvar,string)[1..-2],"NAME"));
    else
      lvar:=FromInert(_Inert_ASSIGNEDNAME(convert(lvar,string),"NAME"));
    end if;

where lvar had value of old pointer. After checking ToInert(eval(lvar)) i found different addresses in

_Inert_LOCALNAME statement compared to "old" lvar.