Re: make i:j equivalent to [(k,k=i,j)]?

highegg wrote:

beliavsky@xxxxxxx wrote:
Would it break anything in Fortran to make an expression

i:j

equivalent to the array constructor

[(k,k=i,j)]

The R programming language, which has a matrix language similar to
Fortran, effectively does this. I know that "not breaking" is not by
itself sufficient reason to add "syntactic sugar" to the language.

Since FORALL supersedes this, I guess this will never happen.
FORALL is less elegant but more powerful.

R has dynamically sized arrays, maybe more like Java's Object
references. You can say:

A <- 1:N

and it will assign to A an array containing the integers 1 through N,
as elements 1 through N. or

A <- 10:20

and it will assign A the integers 10 through 20 in elements
1 through 11.

You can say:

A <- 10:20
B <- x[A]

and it will assign the 10th through the 20th elements of x to B.
That is what you can't do in Fortran with vector subscripts.

You can say:

C <- x[-10:-1]

and it will assign all elements EXCEPT elements 1 through 10
of x to C. Any value of negative subscript will assign all except
that (those) element(s). You can't mix negative and positive subscripts.

y <- exp( (1:10)/10)

will assign exp(0.1), exp(0.2) through exp(1.) to y.

R has more array and matrix operators than Fortran, including
the matrix multiplication operator %*%.

You can also select array elements with an array of logical
values, so either:

x <- y>10
y <- y[x]

or

y <- y[y>10]

will assign only the elements greater than 10, resizing the
array during the assignment.

R has many operations similar to other mathematical interpreted
languages like Mathematica or Matlab.

-- glen

.

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