[Gretl-users] indexes in loops

[Allin Cottrell]

On Thu, 7 Sep 2006, Arnaud Bervas wrote:

> Thanks for your suggestion, but it doesn't seem to work with 
> my script. It doesn't seem possible to make Gretl recognize 
> j=i+1 or $j =$i+1 as a new index...

Please show a little piece of script that demonstrates the 
problem.

Looking at the above, the second variant will surely not work, 
for this reason: when you use the "$" form of a loop control 
variable, it works by "string substitution".  Before the command 
line is parsed, all occurrences of "$i" are replaced by the 
current numerical value of i.  This allows you to use "$i" in 
string contexts such as variable names:

genr foo$i = ...

But it means that in "$j =$i+1", you are trying to assign a 
value to a numeric constant on the left-hand side, as in

3 = 10+1

Allin.