Bell Triangle function problem:

Hello, I am having trouble writing a program that displays the Bell Triangle to the 'n'th row, but I run into a problem when I want the program to return an empty array for decimal inputs. I tried changing my code (see below) but now I get an empty array no matter the input (it worked before).

Prompt: Write a function called bell that returns the first n rows of the Bell triangle, where n is an input argument. For a precise definition, see http://en.wikipedia.org/wiki/Bell_triangle. The function must return an n-by-n array where the top left triangle contains the Bell triangle with each row of the Bell triangle positioned diagonally—bottom-left-to-upper-right—and the bottom right triangle contains only zeros. If n is not a positive integer, the function returns an empty array.

My code:

function B = bell(n)
if n<=0 || isinteger(n)==false
    B=[];
else B(1,1) = 1;
for i=2:n
    B(i,1) = B(1,end);
    for j = 1:i-1
        B(i-j,j+1) = B(i-j+1,j)+B(i-j,j);
    end
end
end

Any help would be greatly appreciated. Cheers!

Answer 1

[Walter Roberson]

tf = isinteger(A) returns true if the array A is an integer type and false otherwise.

If you want to check whether the value is integer, check to see if n == floor(n)

[Amit Tal]

If I understand correctly, floor would round the 1.5 input down to 1. However, I wish the function to return an empty array if the input is not integral. Could I still do that with floor?

[Walter Roberson]

if n <= 0 || n ~= floor(n)
  B = [];

By the way: what happens if someone passes in a vector?