MaplePrimes - answers and comments on Question, recursive procedures with 2 variables

clarify

Joe Riel — Sun, 03 Jan 2010 02:09:48 Z

Probably (i.e. you are missing something). More exactly, we are missing something, the procedure. From the snippet you gave, I'd code it as

f := proc(a::nonnegint,b::nonnegint)
option cache;
    if   a=0 or b=0 then 1;
    else
        f(a-1,b) + f(a,b-1)
    end if;
end proc:

recursive procedures with two variables.

Sun, 03 Jan 2010 02:39:53 Z

Joe,

Thanks! What you suggested works perfectly. I don't have a feeling for the difference

between the use of 'remember' versus 'cache' in recursive procedures.

Ron Graham

option cache

Joe Riel — Sun, 03 Jan 2010 12:02:17 Z

They are very similar. The significant difference is that a cache table has a maximum size, while a remember table can continue to grow. When a cache table is filled, older entries may be replaced with newer ones. You can specify the size of a cache table in the option statement, see ?option,cache. If the size of the cache table were a problem, in the example, you could reduce the required space by sorting the arguments in the recursive call (the function is symmetric).