[PPL-devel] something not clear...

[Enea Zaffanella]

Alessandro Vincenzi wrote:
> Hi,
> 
> i've started to read the ppl documentation, and i've found a doubt
> reading section at page 8:
> 
> 1.4.5 Removing Dimensions from the vector space.
> 
> and in particular, how the remove_space_dimension works.
> 
> In fact from the example i can not understand why applying the operator
> on the singleton set {(3,1,0,2)^T} in R^4 with the variable set {x_1,
> x_2} we obtain just {(3,2)^T}. Namely, i can not understand which is the
> connection between the set of variables gived to the operator and the
> two dimensions removed from P (i.e the second and the third).

In the manual (and in the library itself), the space dimensions are 
indexed starting from zero. That is why removing x_1 and x_2 gives the 
result above. When coding the example above in C++, you will write 
something like

   Variable x1(1);
   Variable x2(2);
   Variables_Set vs(x1, x2);

At a first sight, the manual is clear enough on this respect. Anyway, 
let us know if you find any place where we number the dimensions using 
an inconsistent or ambiguous indexing scheme.

Cheers,
Enea.

> Instead, the remove_higher_space_dimension operator is simpler because
> is easy to understand that it removes all the dimensions  i >= m.
> 
> Thanks,
> 
> Alessandro Vincenzi
> 
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