Ceiling to Nearest 50

I can round the elements of A to the nearest integers greater than or equal to A

ceil(A)

But what about if I want to round it to the nearest 50 greater than or equal to A?

For example, given the following 开发者_开发百科A array,

A=[24, 35, 78, 101, 199];

A subroutine should return the following

B=Subroutine(A)=[50, 50, 100, 150, 200];

You could just divide by 50, take ceil(), and multiply by 50 again:

  octave:1> A=[24, 35, 78, 101, 199];
  octave:2> ceil(A)
  ans =

    24    35    78   101   199

  octave:3> 50*(ceil(A/50.))
  ans =

    50    50   100   150   200

An easy way is to just add each number's complement modulo 50:

octave> A = [24, 35, 78, 101, 199] 

octave> mod(-A, 50)       # Complement (mod 50)
ans =

   26   15   22   49    1

octave> A + mod(-A, 50)   # Sum to "next higher" zero (mod 50)
ans =

    50    50   100   150   200

octave> A - mod(A, 50)    # Can also sum to "next lower" zero (mod 50)
ans =

     0     0    50   100   150

(Note that this only depends on integer arithmetic, which avoids errors due to floating-point rounding.)