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Blitz Support : |
From: Julian Cummings (cummings_at_[hidden])
Date: 2004-09-09 12:37:38
Hi Eddie,
Assuming that the scalar is a constant for the entire array operation,
the most straightforward way to do this is to convert your function into
a functor (a struct with an operator() that performs the operation on a
pair of elements from the two arrays). The constructor for your functor
would take the scalar as an argument and store it. Something like this:
// original function
double foo(double a1, double a2, double scalar1) {/* ... */}
// new functor
struct functor {
double scalar_m;
functor(const double& scalar) : scalar_m(scalar) {}
double operator()(double a1, double a2) { return foo(a1,a2,scalar_m); }
BZ_DECLARE_FUNCTOR2(functor)
};
The BZ_DECLARE_FUNCTOR macro will allow your new functor to operate on
blitz Arrays just like the BZ_DECLARE_FUNCTION macros do for functions
(see the header file <blitz/array/functorExpr.h> for more details).
Just construct an instance of the functor with the scalar value and
then apply the functor to your Arrays.
We could produce a BZ_DECLARE_FUNCTION3_SCALAR macro, but the
combinations start to get a bit cumbersome at this point. You have to
handle all the possible combinations of two Arrays and one scalar or one
Array and two scalars. I recommend using the functor approach to handle
scalar parameters within an Array function.
Regards, Julian C.
Eddie.Breeveld_at_[hidden] wrote:
>Dear All,
>
>There is a "#define BZ_DECLARE_FUNCTION2_SCALAR(name, sca)" definition
>within Blitz - how easy would it be to implement a ternary equivalent?
>
>We would like to have a function that operates element wise on two arrays,
>and uses a scalar to modify the operation. e.g.,
>Function(Array1,Array2,scalar)
>
>Is it simply a combination of the BZ_DECLARE_FUNCTION2_SCALAR and
>BZ_DECLARE_FUNCTION3 declarations?
>
>All the best,
>Eddie
>
>____________________
>Edward Breeveld
>eSolutions
>Watson Wyatt LLP
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-- Dr. Julian C. Cummings E-mail: cummings_at_[hidden] California Institute of Technology Phone: 626-395-2543 1200 E. California Blvd., Mail Code 158-79 Fax: 626-584-5917 Pasadena, CA 91125