I want z  to becomes abs(z) then later on, remove abs() and obtain z back in the same form it was.

I found that Maple changes z when I put it inside abs. Like this

expr:=(-y^2+1);
abs(expr);
op(1,%);

So instead of 1-y^2, I end up now with  y^2-1. I want to keep the same expression I started with.

Mathematica does not do this:

expr = 1 - y^2
Abs[expr]
%[[1]]

Is there a way or option to tell Maple not change the expression when I put it inside abs()?

This complicates what I am trying to do in Maple.

thank you

What is the correct idiom in Maple to do subexpression replacement?

Suppose I want to replace each occurance of ln(anything) by ln(abs(anything)) in an expression.

Currently I call indets and then loop over each entry and use patmatch to do the replacement.

Is there a better method than what I doing now? Here is an example

restart;
expr := 7*ln(arcsin(x))-(1/2)*ln(x-1)*sin(x)-(1/2)*ln(x+1)+f;
lis:=indets(expr):
for z in lis do
    a:='a';b:='b';c:='c';
    if patmatch(z,a::anything*ln(b::anything)*c::anything,'la') then
       map(z0->assign(z0),la);
       expr:=subs(z = a*ln(abs(b))*c, expr);
    fi;
od:
expr;

I do not know if this will fails on some other cases yet.

I found that when changing constant of integration from _C1 to C1, Maple now fails to verify solution.

Is one supposed to only use constant with _ in it for this? I prefer to use C1 instead of _C1. Why does Maple odetest fail in this case? Is there a way around this?

Here is an example

restart;
ode:=diff(y(x),x)=x*ln(y(x)):
implicit_sol := -Ei(1, -ln(y(x)))+C1=(1/2)*x^2;
explicit_sol := solve(implicit_sol,y(x)):
odetest(y(x)=explicit_sol,ode);

Now changing C1 to _C1 and nothing else, odetest verifies the solution

implicit_sol:= subs(C1=_C1,implicit_sol);
explicit_sol := solve(implicit_sol,y(x)):
odetest(y(x)=explicit_sol,ode);

I understand the using symbol with _ is a convention in Maple for global symbols. But I want to use C1 and not _C1 as it is easier to read.

I want to check that all entries in a list are of some value. Say 0. (or in general, if all entries satisfy some condition).

So, If any entry is not zero, then it returns false. It returns true only if all elements meet this conditions.

What would be the right way to do this in Maple? I know I could write a loop. But I am asking if there is a build-in function in Maple. Here is an example

ode:=y(x)*diff(y(x),x)=x*(y(x)^2+2):
sol:= dsolve(ode,y(x)):
check:=map(z->odetest(z,ode1),[sol]);

                       check := [0, 0]

I want to check that all entries in check are zero. This tells me all my solution are correct.

I can't use member(check,0) since this only check if at least one entry is zero. I want to chek that all entries are zero.

In Mathematica, it has AllTrue function. Like this

check = {0, 0, 0};
AllTrue[check, # == 0 &]

     True

The "#==0&"  is the test to do. It uses this test on each element automatically. If all satisfy this test, then it returns true.

Again, I can easily write a small function in Maple to do this,

alltrue :=proc(arr,value)
    local z;
    for z in arr do
        if z<>value then
           return(false);
        fi;
    od;
    return(true);
end proc:

alltrue(check,0) return true.

But I am asking if there is a build-in such function similar to the above one in Mathematica, which accepts a more general test function to use.

why

expr:=1-3*y;
patmatch(expr, b::integer - a::integer*y,'la');

gives false but

expr:=1-3*y;
patmatch(expr, b::integer + a::integer*y,'la');

gives true?

Should one then use `+` for matching with `+` and `-`? This result was a little confusing to me. 

It is actually good that it behaves this way. Makes it easier to write the pattern (less cases to cover). But I would have expected both to return true, that is all.