Calculating product from rows - (aggregate product )

Hi

I would like to calculate a product of a field's values of a relation,
this function may multiply each value and give the result as a single
float number.

For example:

CREATE table imaginary(id INTEGER NOT NULL, some_field FLOAT
NULL,primary key(id));

INSERT INTO imarginary(1,0.333);INSERT INTO imarginary(2,0.667);INSERT
INTO imarginary(3,0.4);

SELECT prod(some_field) FROM imarginary;

would give 0.0888444 (which is 0.333*0.667*0.4)

Is there an already existing function that does this.

Allan.