Local variables in a function definition can be given initial values in the line they are declared in by putting their initialization in parentheses; for example,
local a,b; |
a:= 1;
|
is the same as
local (a:= 1), b;
Local variables should be given values within the function definition. If you want to use a local variable as a symbolic variable, then you can indicate that with the assume command (see Section 5.4.8). For example, if you define a function myroots by
myroots (a):= { |
local x; |
return solve(x^2=a,x); |
}
|
then calling
will simply return the empty list. You could leave x undeclared, but that would make x a global variable and could interact with other functions in unexpected ways. You can get the behavior you probably expected by explicitly assuming x to be a symbol;
myroots (a):= { |
local x; |
assume(x,symbol); |
return solve(x^2=a,x); |
}
|
(Alternatively, you could use purge(x) instead of assume(x,symbol).) Now if you enter
you will get
| [−2,2] |