How do i get the index position of a multiple number from an array?

Hi My array is

A=[300 500 900 100 1800 34 400 600 2700 450]

I want to get the index of the multiple of 900 i.e 900,1800,2700

Index=find(A==900)

Any way of modifying it to get the index of the multiples?

Answer 1

[per isakson]

Seems to do it

>> is = arrayfun( @(num) mod(num,900)==0, A )
is =
     0     0     1     0     1     0     0     0     1     0
>> A(is)
ans =
         900        1800        2700

>> ix = find(is)
ix =
     3     5     9
>>

or better

>> is = mod( A, 900 ) == 0
is =
    0     0     1     0     1     0     0     0     1     0

Answer:

Index = find( mod(A,900) == 0 );

[yashvin]

Awesome! I have one more question. I do not know whether the mod function can be used. Assumming I have an array like

B=[0 4 8 12 16 20 24 28 32 36 40 43]

I want to get the starting and ending index for a multiples of 8.

For example

Value=0   Index=1  % stating index

Valye=8   Index=3   %ending index

Value=12  Index=4   %starting index

Value=20  Index=6   %ending index

Value=24 Index=7    %starting index

Vale=32  Index=9    %ending index

Please note the last number is not multiple of 8.

[per isakson]

I don't get it! 12 and 20 are not multiples of 8.

[yashvin]

I am sorry for the confusion. Actually, you right. It is not multiples. It is increment by the value 8.

For example, starting with the first number, I get the index and find the index of the next number which is an increment of 8. Again, start with the next number, then find the index of the next number which is an increment of 8.

Value=0   Index=1  % stating index
(increment of 8)
Value=8   Index=3   %ending index

Value=12  Index=4   %starting index
(increment of 8)
Value=20  Index=6   %ending index

Value=24 Index=7    %starting index
(increment of 8)
Vale=32  Index=9    %ending index

Any way we can get the the starting and ending index values for a general case ?

[yashvin]

In simple terms, given the array, extracting the starting and ending index of numbers which is an increments of 8.

0-8
12-20
24-32

[per isakson]

I didn't read, however this might do it.

>> [ix1,ix2] = cssm
ix1 =
     1     4     7
ix2 =
     3     6     9

where

function [ix1,ix2] = cssm
    B = [ 0 4 8 12 16 20 24 28 32 36 40 43 ];
    ix1 = 1;
    ix2 = [];
    while true
        ix = find( B(ix1(end):end)==B(ix1(end))+8, 1,'first' ) + ix1(end)-1;
        if isempty(ix)
            break
        end
        ix2(end+1) = ix;
        ix1(end+1) = ix+1;
    end
    ix1(end) = [];
end

There is certainly potential for improvements.

[yashvin]

Let me check!