MaplePrimes - answers and comments on Question, Variable's hidden evaluation

reverse the order of operations

acer — Wed, 27 Feb 2013 21:47:17 Z

In your example, `c` has been assigned the value that you see. The fact that the value came from evaluating a+b is lost (except mathematically, but you don't seem to be wanting that), by which I mean that in your example the literal 'a+b' is not a part of the value assigned to name `c`.

If you reverse the order of operations, then yes you can evaluate `c` to one level, and get the unevaluated 'a+b'.

> restart:

> c:=a+b;

                                  c := a + b

> a:=5*x^2-3*y^3:
 
> b:=3*x^2+10*y^3:

> c;

                                     2      3
                                  8 x  + 7 y

> eval(c,1);

                                     a + b

In my example above it is full evaluation of `c` that produces and displays that expression in x and y.

Another variation is,

> restart:

> a:=5*x^2-3*y^3:      
> b:=3*x^2+10*y^3:     

> c:='a+b';

                                  c := a + b

> c;

                                     2      3
                                  8 x  + 7 y

> eval(c,1);

                                     a + b

You could also study the evaluation rules within procedures, which differ from those for the "top level." The manuals should help here.

You might also consider the somewhat related topic of command history.

acer

eval(c,1) etc.

Preben Alsholm — Wed, 27 Feb 2013 21:50:35 Z

The way Maple works this is not possible as you entered the commands.
No problem if you defined c before a and b or if later you defined c:='a+b'.

restart;
a:=5*x^2-3*y^3:
b:=3*x^2+10*y^3:
c:='a+b';
c;
eval(c,1);
restart;
c:=a+b;
a:=5*x^2-3*y^3:
b:=3*x^2+10*y^3:
c;
eval(c,1);

So always use '

Christopher2222 — Wed, 27 Feb 2013 22:21:28 Z

So would it then be wise then for everyone assigning values to use the uneval form in everything?

no

acer — Thu, 28 Feb 2013 05:44:21 Z

No, it would be very unwise.

acer