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Array parameters are specified by a [number] after the parameter name, where
number must be an integer. In your parameter file you can specify them
with something like
foo::bar[9] = 99
(note it is C numbering, starting at 0).
In your source code they appear as arrays, bar() in Fortran, starting at 1,
and bar[] in C, starting at 0.
Accumulator parameters are parameters whose value is built up from the value
of other parameters. The other parameters don't need to be known about by
the thorn providing the parameter.
The syntax is:
base parameters are defined like
REAL foo "The foo parameter" accumulator=(<expression>)
{
(1:500 :: "Anything greater than 1 and less than or equal to 500"
} 72
and parameters which modify this one's value would be like
REAL foobar "The foo parameter" accumulator-base=foo::bar
{
22:65 :: "Sensible number"
} 42
<expression> is an arbitrary arithmetical expression involving the old
value of the parameter,refered to as 'x', and the parameter which is
modifying it, refered to as 'y'. E.g. x+y, x+(1/y) x*y, x+y^2, x/y,...
The expression should commute when applied twice, i.e. for expression
L(x,y), we should have
L(L(a,b),c) = L(L(a,c),b)
(This allows people to use x/y as an expression which would end up as
a/b/c = a/c/b .)
To add a value to an accumulator parameter from another implementation, you need
to USE or EXTEND that parameter first.
As a more complete example, to provide a parameter which is the sum of the
squares of other parameters, you can say
REAL squares "Sum of squares" accumulator=(x+y^2)
{
0: :: "Any non-negative number"
} 0
Then, someone in another thorn can add to your squares by saying
USES REAL squares
REAL mynumber "My number" accumulator-base=foo::squares
{
0 : 45 :: "Some numbers"
} 3
Then, when these thorns are activated, the value of foo::squares will be 9
(0 + 3^2).
Tom
git-svn-id: http://svn.cactuscode.org/flesh/trunk@2830 17b73243-c579-4c4c-a9d2-2d5706c11dac
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